maybe you can make it reversible by refunding it on the same terms, i.e the buyer has the right to return the good to the seller, and the seller pays 2X or 0 with prob 1/2 to the buyer.
Maybe, but a) there may be statutory rights issue, b) this just seems likely to annoy people and c) you might run the risk of actually having to comply with gambling laws if you take money from people and offer them a chance of doubling it.