The person selling the account should be vague in describing the account so that there is a large number of accounts they could possibly be selling. For example instead of saying an account was registered in June 2013, has 252 activity and 1300 posts, a seller can say that the account was created on or before August 2013 (or in the first half of 2013), has 250+ activity and 1,000+ posts.

It is more difficult to protect against timing attacks on auctions however in auctions the seller could wait an hour or two to change the password however this will only provide limited protection.

If you are selling on a "normal" thread then you can keep the account listed for several days after selling the account.