The New York Times tried to make the case that third-party guarantees, or 'irrevocable bids' as they are styled at Sotheby's, have the effect of suppressing bidding.

One of the problems with that conclusion is that it may simply reflect confirmation bias. In other words, the works that show strong interest from bidders may be the very lots that auction houses are unwilling to give the terms that come with these arrangements because they are confident with the risk.

However it plays out, Sotheby's doesn't believe one can come to any conclusion from the performance of the various lots. They provided us with a breakdown of each type of guarantee for each sale.