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davidcyclebackAli, again I'm no wax pack expert, but the experts look at stuff like paper consistency and pattern at point of seal, gloss at point of seal, angle of corners due to resealing, etc. If you heat reseal a wax wrapper, it can change the gloss and consistency of the wax paper. So there are technical things they look at, not just if the paper is folded up nicely or there are tears.
When it's factory folded wax paper-- the emphasis on wax paper--, changes, refolding, resealing and such can be detected by close examination and experience. The wax is sensitive to changes and can hold a record of what's happened to the wrapper.
I know one key point they look at is the angle of the edge of the pack (the edge of the thickness). Packs were factory sealed en mass and will have consistent angles. A resealed pack will often have a very different folding angle, in particularly when the resealer wasn't paying attention to that detail. One of the simple things a beginner can do is to compare the edge folding angles-- this will identify many suspect packs.
Mark "The Baseball Card Kid" Murphy, who used to be the head pack grader for GAI, has a nice color illustrated guide to wax packs, including how to judge authenticity of packs, the details of identifying resealing, etc. He goes over in better detail many of the points I mentioned above.