If bids are non-binding on eBay Motors, then that means people can bid for entertainment and decide not to follow through if they don't feel like it. That certainly can amount to a big waste of time for sellers. It makes eBay seem like a pretty stupid venue to sell cars.
So nothing keeps anybody from making high bids on any cars they might see Fred Hass Toyota in Houston trying to sell from now on. And then after the bid's over just saying, "oh, never mind."