I don't advocate this, but, when I used to collect these back in third gen, there would always be several opened packs hiding behind the other stuff on the shelves; kids were (somehow avoiding the security mirror ~_~) opening packs, taking the exes out, and leaving the remaining 'trash' behind, the other eight cards or whatever. I always reported this, but I was too stupid to claim the other eight for myself since they were just sitting around and, then, collected back by the store...it does happen.
Now, I may just have to go buy a few packs and try Mence Master's little trick to see if it works for me xD...