Well one of the obvious don'ts is do not UNDER ANY CIRCUMSTANCES pay ANY money upfront to a resales agent. (They should expect to get a %age of the sale - probably around 15%). There are mutliple scams going around to cream off yet more money from unsuspecting punters, under the guise of tax prepayments, transfer fees etc etc, which do not result in any sale, and merely extract more hard-earned cash.
Another scam is selling you another week under the guise of swapping your week for another - you end up with two weeks.