When few chips of a type are known, say 10, but then grandpa dies and his descendants find the other 190 in the attic and put them on ebay...well you get the idea. I haven't been in the hobby long but I've already seen it several times. The Golden 10c Reno chips and Harold's Club $500 chips come to mind. Rick from Pawn Stars has talked about how he doesn't even touch rare casino chips anymore in his shop because he's been burned so many times.