A mishna on Erchin 27a discusses buying land back after it has been consecrated. It says that if one offered ten selas, another twenty, etc. up to one who offered fifty, and then that last guy retracted his bid, he owes the difference between his bid and the next-lower one and then the next-lower one is the buyer. If he retracts too, iterate. If the original bidder retracts, they sell it on the open market and he owes the difference between the price they got and his bid. That all sounds straightforward and fair.
I am assuming that these kinds of transactions were uncommon, single events. My quesion is: does this process also apply to modern auctions where many items might be auctioned and only at the end the money is settled? Or, for that matter, participating in simultaneous auctions on eBay? Once I have been out-bid, do I still need to keep that money in reserve in case the people above me retract, or (per Jewish law) is that not my problem because that would be impracticel in auctions structured as they usually are now?
(I don't actually participate in auctions this way and would consult my rabbi if this mattered, but I was curious upon reading this mishna.)