There’s definitely risk to the buyer if the price moves against them.
In the US equities markets, all trades are ultimately settled by the DTCC. In turn, they only allow members to settle trades. Every stock trade on an exchange (as opposed to a purchase from a dealer) will be settled between two clearing broker members of the DTCC on behalf of their clients. In the event of a settlement failure, the clearing broker assumes the risk,
On Settlement day, if a counterparty doesn’t deliver their side, the broker must make up the economic difference. The DTCC in turn requires brokers to post collateral to make sure they can cover their clients.
So if a trade happens at $100 and on settlement day the seller doesn’t deliver the stock and the price has gone up to $120, the seller’s clearing broker must step in and pay the $20.
On the sneaker exchanges, buyers and sellers serve as their own brokers and so any collateral should be paid by them. Since a buyer must deliver payment on trade date (your card, PayPal, etc.) there is asymmetric settlement risk. The buyer essentially can not default, but as we’ve seen the seller can and frequently does.
I get that this is super arcane, but the guys who set up the sneaker exchanges (especially Stock-X) definitely understand all this. They have tried their best to emulate equities markets in all other respects. They just refuse to implement this because they know it’s not commercial.