I remember when it was customary in our club (with well-known, respected chip dealers and those new to the hobby) that if and when a box/quantity of the previously sold chips popped up, either a credit was issued or the seller 'contacted' the buyer in order to either return the purchase price or work out some sort of deal.

In my opinion (and I'm quite sure in the opinion of others as well) there are many aspects of a sale; as I do not believe it's as easy as a 'done deal' as others claim it is.