THIS ^^ is actually the biggest problem with account sales, but as said before: removing all addresses posted by the account won't help you (because of the archives and quotes).
It is the reason why you should use a trusted escrow to look over any account you wish to buy, in order to keep the risk of this happening as small as humanly possible.
so better i use signed message like this :
so excrow can verif it too..? right
That would be a good message... make sure the seller signs is with a STAKED address, at least a couple months old.
That way, you can at least prove you own the account in case the seller ever tries to reclaim the account after he sold it to you.
Such a signed message is insufficient when proving the account actually changed hands, because there's always a possibility both the seller and the buyer are the same person, and they used an escrow service to make the sale look legit.