Articles and Tips
Let's be careful out there!
I suspect this is more of a problem in the baseball card collecting world as they tend to have rare "valuable" cards mixed with much less valuable common cards - not as much an issue with nonsport collecting but we are certainly not immune to this!
Here's a link to an article about recognizing resealed and fake packs from the wacky package website - a really nice website - well worth checking out!
Here's another interviewing Steve Hart from Baseball Card Exchange (primarily baseball oriented but still interesting)
Another discussion from Collectors Universe
Another discussion on net54