... is allowing a fellow collector to purchase a chip that you wanted only to see it up on ebay 6 months later.

This happen to me at the convention a couple of years ago. I picked out several chips that I was going to purchase. Before I actually bought the chips, a fellow collector/DEALER asked if he could buy one of the chips. I knew he was a big collector of that particular casino. Stupidly I allowed him to buy it only to see it later on on ebay (and go for a ridiculous price)