From the CC>CC Code of Ethics:

10. To offer on all sales and trades, a 10-day return privilege on any item purchased or traded, unless I have clearly and conspicuously stated that items are sold or traded "as is," and without a return privilege.

If the individuals had a table at the convention, then they have to be members of the CC>CC and they are subject to the Code of Ethics. I recommend making a claim with the Club to have the deal undone.