No idea. I wouldn't have thought that it's an auction is of any relevance. The reason given for the cooling off period is because you are unable to inspect the goods, which is as relevant for auctions as anything else.
Anyhow, I've just told a US vendor that I'm not taking up an item I bid on, on Ebay's UK site, since there is no reasonable way I can get the money to him. No reply, as yet....