Perhaps SE shouldn't refund all of the losing bidder's money. Perhaps they should only refund, say, 95% of it. Anyone who can afford to put down 5, 20, or 50 million for a chance at a house can afford to lose 5% of it.

Because right now, people bid on house knowing they have nothing to lose by doing so.
Imposing a small fee on the losing bidders might reduce the number of people bidding to those that really want a house, and discourage people from creating multiple accounts just so they can take more no-risk attempts to get a house.

Plus, removing gil from the game is never a bad thing.