In my experience, 99% of chip sales/trades are without stipulations on resale. The exception may be when multiples of a find are sold to buyers and dealers at an orderly price(s) with the understanding that the price is supported at that level for a while.

It's really not possible to attach "strings" to an ebay sale, IMO. A sale with stipulations would need to be worked out personally between the parties.

Your question reminded me of a lawsuit going on in the art world about a sale stipulation regarding confidentiality. It involves a piece valued at $31.4 million at its most recent sale -- so that's a completely different ballpark to the chip sales we do in this hobby!!

If interested in the lawsuit, click on:
http://grossmanllp.com/art-law-blog/2013/02/lawsuit-over-confidential-sale-of-rothko-masterpiece-continues-highlighting-the-need-for-proper-contracts-in-art-sales/