IMHO the buyer has no right to return the chip unless there was some sort of agreement on returns before the sale was consumated.

The seller's moral obligation depends on his/her own conscience and whether they think there is a chance the buyer was in any way mislead or uninformed about the established market price for the chip--whether the seller had an advantage in knowledge of chip values over a naive buyer.

It seems to me that chips in this price range tend to fluctuate in sales price a lot depending on the seller's motivation and other circumstances.

So, if I sell a chip today for $1,200 and tomorrow somebody decides to liquidate their collection at fire-sale prices, should I offer my buyer a refund? No.

Knock a couple of decimal places off the prices and it's much easier to decide: $12 -vs- $7 price difference happen every day in chip sales.

Just my opinion.