I used to wait till the last minute.
Now, I just hit them with a neg and expect a neg in return. <shrug> I don't like getting them but in the scheme of things...it warns other sellers to be wary of this buyer.
Usually when I hit them with a neg, they are more than happy to do a mutual withdrawal. The comment from my negative is still sitting on their feedback even though the neg isn't.
Good Luck,
Donna