If you implemented something where you were FORCED to give your In-game names and update it with checks done every so often or an auto mated system or whatever. Also make it like a list of account that you own, and that any other account name is not yourself.
That means if you change your name and dont update it and your old name was taken it would be your fault and could not be held reliable.
Example In a signature
"ONLY TRADE WITH "accountname123", "accountname234", "accountname345"
that would let you have a list of names and previous names and then you could prove that it was taken if it was, as a changed name always has a "previous name when hoevered over their current name in game on a friend or ignore list.
It might be difficult or might be easy but thats my opinion and if you could do that, it would provide a large amount of security, or the very least know who scammed.