There is an issue faced by this site and others like it:
  Any resource designed to educate collectors, can also educate counterfeiters.

  For that reason, one or two of the most important tips presented here are incomplete.
  In particular, it would be VERY useful for this site to include photos of the back sides of authentic mini-marquees, for collectors to compare against. However, that would offer counterfeiters a one-stop resource for fine-tuning their fakes to look just like the authentic mini-marquees.
  This isn't meant to be a slight against sellers who do show images of the back, as that is necessary in order to advertise the likelihood of authentic goods. But sales pages are transient, while this page is both long-term and conglomerates most titles into one location on the internet.

  To strike a balance between utility and safety, most of the tips offered here fit into one of these categories:

1. Tips to help point collectors in the right direction to discover information for themselves. Those who are interested can invest time to gather a little data on the specific titles they're curious about, using the info on this site as a guide.
   The hope is that many counterfeiters won't invest that money/time/effort, because presumably most of them are after a quick buck and there are still plenty of uninformed collectors out there who these terrible people can swindle.
2. This site also offers info on what is standard across most titles, vs which titles break those standards. These tips are meant to prevent non-standard artsets from being mistaken as fakes. The last thing we need are authentic artsets being tossed into the trash.
   Examples of this include the build of the stickers, single vs double-sided softdip sheets, the existence of variant printing runs, etc.
3. Information which is already apparent through photos of the front side of the artset items. For example, the language color-codes used by the soft-dip sheets.

  Because it is always possible for a counterfeit to be indistinguishable from an authentic item, these tips help to greatly increase confidence in authenticity, but they cannot establish 100% certainty.

• Check to make sure that the mini-marquee matches what is listed in the "Marquee Type" column of the table on this site's home page.
• The primary way to judge a mini-marquee's authenticity is to examine the particulars of its reverse-side.
    For the safety reasons mentioned above, this site does not provide images of the reverse-side of the mini-marquees. To check yours, it may be necessary to do a small amount of surveying for other examples of the title you are checking. Things to keep in mind when comparing the back of your mini-marquee to others:
  
  1. For mini-marquees which appear uniformly-lightened on the back ("L" mini-marquees):
       The quality to check for is exactly how lightened it appears on the back, which is a quality that depends on the title's release date, with only a few exceptions. This quality is referred to by this site as the mini-marquee's lightness-rating. Pristine specimens of the same title will have the same lightness-rating (within a slight margin of error), unless they are from different printing runs (as detailed on the table).
       The information linked to in the "Data Totals" column of this site's table includes remarks on if a title released immediately before or after the title in question shares the same lightness-rating (as evidence of it following timeline trends). A collector might make use of this information if they have access to that neighboring title.
     
     Comparing physical samples: Comparing the lightness-ratings of two physical mini-marquees of the same title & print is straight-forward: They should look identical from the back if they are both pristine.
       Be aware that there is a minor margin-of-error when comparing the lightness-ratings of two mini-marquees. This is to account for human error, subtle yellowing differences, and the like. So if two mini-marquees differ in lightness only very subtly, then it may be safe to treat them as a match.
       If one is trying to compare the lightness-ratings between physical marquees of different titles, then it's best to compare areas of black ink. As it's a common color shared between titles.
     
     Comparing against a photograph: Photos cannot be depended on to accurately represent a mini-marquee's brightness. This is due to the processing done by the camera, the lighting at the time the photo was taken, and the monitor it is viewed on. The same is true for the photo's saturation.
       Instead, the data suggests that a somewhat safer approach is to examine the contrast. Although note that the variables mentioned above do alter this as well, so it is still error-prone. Furthermore, it is difficult/impossible to differentiate contrast between samples whose lightness-ratings are somewhat close.
       Keep in mind that for "L" marquees, they have more contrast when placed against a white background compared to dark or even off-white backgrounds
       A yellowed marquee will generally have less contrast than a pristine sample. Although be aware that in some cases fading can increase contrast in some areas, and sometimes the presence of yellowing makes it hard to discern if a mini-marquee has had any fading.
     
     Yellowing's effect on lightness-rating: A yellowed mini-marquee is more difficult to assess. Part of this chaos may be due to yellowing, and part of it may be due to fading. The presence of fading might be hard to spot due to the yellowing, creating an unknown combination of the two effects which might result in different lightness-ratings between two otherwise seemingly-similar specimens.
       Assuming one measures lightness-rating based on the areas of black ink, even minor yellowing can shift a mini-marquee's lightness-rating by 1-2 points either lighter or darker (depending on the title). Or in some cases even heavy yellowing might not change its lightness-rating at all. And two mini-marquees of the same title/print which seem like they might be yellowed by the same amount can still have slightly different lightness-ratings from one another.
       Furthermore, yellowing/fading can be subtly non-uniform, resulting in different lightness-ratings within the same sample.
       Although, one can generally eyeball if a yellowed mini-marquee is "near enough" to how one might expect that title to appear if it were yellowed. Still, whatever the exact lightness-rating was for a specific sample prior to it being yellowed remains uncertain.
     
  2. For mini-marquees which appear somewhat like a photo-negative on the back (what this site calls "Variable-Opacity" aka "VO" mini-marquees):
       Simply check if the marquees being compared have the same "VO" pattern. Also check the "Data Totals" column of this site's table for information on second prints, as they sometimes have a different "VO" pattern.
       When viewed from the back, "VO" marquees have more contrast when placed against a dark background compared to a white background, thus the VO pattern is easier to see when against a dark background. A yellowed marquee may have different contrasts in its pattern compared to a pristine marquee. The data also suggests that fading/yellowing might cause areas of mid-opacity to appear lighter than normal (when viewed from the back).
       Be aware that it is very common for the opacity layer to be slightly misaligned from the color layers by a fraction of a millimeter. This can result in dark or light edges along the VO pattern for some mini-marquees. This misalignment is NOT consistent between all mini-marquees for the same title. I have also come across one (and only one) physical sample which had considerable misalignment of its opacity layer from the color layers (by 1.5 millimeters), which caused the mini-marquee to appear double-imaged when backlit. That specimen was from "Robo Army."
  3. For "Bust-a-Move" and "Power Spikes II" ("Fragile"/"F" mini-marquees):
       Most (but not all) specimens will have many, very thin scratches on the back which are visible when the mini-marquee is backlit.
       Since the back is uniformly slightly lighter than the front, the same process as is used for "L" mini-marquees (above) apply here.
  4. For titles with official, paper mini-marquees ("P"):
       The somewhat glossy paper used is of the same type which is used for the authentic fliers of most titles.
  5. For titles with glossy-lightened mini-marquees ("GL"):
       The back is just as reflective as the front. IE: It does not diffuse light the way the back of an "L" mini-marquee does.
       Since the back is uniformly slightly lighter than the front, the same process as is used for "L" mini-marquees (above) apply here.
       It's ok/expected if some individual [GL] mini-marquees have a little white along the edges (less than a millimeter).
• The backs of some fake marquees are slightly blurrier than the original. This is easier to spot with black text against a light background.
• If a mini-marquee has "Not for Sale" written at the bottom, then it is not an original, MVS mini-marquee.
  Such mini-marquees were released as part of the "NeoGeo Online Collection" for the PlayStation 2. This site has only been able to survey the backs of 2 such mini-marquees (for "Galaxy Fight" and "Waku Waku 7"), both of which had a "VO" construction. From the back, they did have different VO patterns than their authentic counterparts, but the differences might be easy for some collectors to miss.

• Check the title's entry in the table on this site's home page, to see if it has an authenticity sticker. If it does, and if the artset has at least one sticker-strip, then the auth-sticker will be attached to one of the set's sticker strips. Also check the notes in the table for exceptions.
    Fakes which use photocopies/scans of the sticker will of course have the auth-sticker's image be a part of the same image of the sticker-strip (IE flush with the paper), and it will not change its holographic image as its viewing angle is changed.
• Most stickers have rounded corners, except where noted otherwise in the table.
    Folks who scan/print fake stickers sometimes leave the corners angled, showing their scanner's background in the empty space.
• Most stickers have a backing which is light-green and waxed. This backing also is split into 2 pieces.
    Again, exceptions to this are listed in the table's notes.
• The backing is just as tall as the sticker. (Although the backing can be longer than the sticker.)
  Of course, it might be the case that the backing isn't aligned, and so juts out above or below the sticker. But the total height should still match.

  Paper items are the easiest to fake. Still, there are some qualities to check for.

• Check the title's entry in the table on this site's home page, to see if it has an authenticity sticker. If it does, and if the artset does NOT have any sticker-strips, then the auth-sticker will be attached to one of the set's fliers.
    Fakes which use photocopies/scans of the flier will of course have the auth-sticker's image be a part of the same image as the flier (IE flush with the paper), and it will not change its holographic image as its viewing angle is changed.
• It is printed on somewhat glossy paper. That is, it has a sheen to it, like a magazine's pages.
  Note that water/mildew damage can decrease the sheen.
• The fliers were cut from printouts which had "bleed": the art extends beyond the location of the cut, to ensure that the entire flier contained artwork.
    This means that there are a few qualities to look for which can potentially differentiate an authentic flier from a simple, "scan-print-and-cut" counterfeit:
  • Authentic fliers should not have art-less space abruptly appear along any of the edges, unless it is obviously a part of the design.
  • It's ok if a flier's art seems cropped by a millimeter or two along one or two edges when compared to another flier for the same title. That is the result of the edges being cut at a slightly different location.
      However, it is unlikely that the art would be cropped along all 4 edges. That suggests the possibility that a counterfeiter may have cut it too small, or that the image itself was slightly magnified.
      Although there is variance in flier size within the same title, my limited observation is that such variance within a title is plus or minus 1 millimeter (possibly a little more when comparing 2 different titles). However, I only measured 60 pairs of fliers across 10 titles (ranging in release dates from 1991 to 1999). So that observation should be taken with a grain of salt when trying to apply it to all titles.
    
    A noticeable example of exposed bleed-art can be seen in this site's photo for the English set of "Puzzle de Pon." The left and right edges of the title flier in that photo are off by 2.5 mm in their cut position, causing the left side to appear truncated and the right side to expose 2.5 mm worth of bleed art. That is the largest misalignment observed in this site's survey for the fliers of any title.
• If it is one, larger flier, check the "notes" section of this site's table to make sure that it is supposed to be a single, fold-out flier rather than two fliers.
    Sometimes counterfeiters will scan two small fliers onto the same printout, creating a larger flier.

  Paper items are the easiest to fake. Still, there are some qualities to check for.

• These are color-coded by language and manufacturer. A summary of these colors is provided in this photo. Major exceptions are mentioned in the "notes" column of the table on this site's home page.
  Although note that the table does not mention those cases where a title has a subtly different shade of the standard color. For example, a small number of titles (including about 1/3 of the ADK titles) have a slightly darker shade of blue for the English softdips, and some of the later titles have subtly more saturated hues for multiple languages.
  Also be aware that, due to wear and fading, the exact shade of a color can vary between specimens.
• Softdip sheets are double-sided. Exceptions to this are listed in the "notes" column of this site's table.
• It's ok if some, folded softdip sheets are a little wider and/or taller than the fliers. The softdip-sheet's size varies between titles, but seems to be consistent within a title (although I have not rigorously checked this claim). I also have not checked if the size of the softdip sheet follows trends in the release timeline.

  I haven't cared enough to analyze this one.
  However, there are some things which I've casually observed.

• The earliest titles had bags which were wider than those of later titles.
• "King of Fighters 2001" has sturdier bags than normal.
• The same type of bag is used for all languages of a title.
  Be aware that some sellers add their own type of bag to a set. Some popular sellers in Japan do this, which might mislead a collector to believe those bags were originally shipped with Japanese kits.