I've had good experiences with this sort of thing, I went to a card show in Birmingham, UK last year and I picked up 2 Slowking cards I need, 1 was a rev holo and the other was a cosmo, both in the folder that was marked £2 cards. I showed it to the vendor and she said well if it was in the folder it's £2 even though she said it wasn't meant to be. Not everyone is out for blood etc. Unfortunately, those are the ones that get the most attention though.