I think with the current systems in place, scalpers actually can afford to buy arbitrarily large numbers of GPUs. Credit cards exist, as well as a lot of other ways to borrow money short-term.
They have a bot buy and relist all available stock as fast as possible, sell as many as they can in 2-3 weeks, and then return all unsold stock before they need to make payments. There's a lot of financial motivation and not that much risk, so long as a retailer will let somebody return a lot of graphical cards for free; or more likely one person using dozens of accounts to return a couple at a time.
Restocking fees and short return windows would help make that move more risky, but as a normal customer I don't like that solution.