He doesn't have to provide squat. Since you are claiming that account changed the owner, its you who has to prove that, burden of proof is on the one that makes the claim.
Yeah, sorry for me trying to avoid some newbie getting scammed. Its me who should be targeted here.
Lets wait until someone will get scammed and then maybe some reputable member will ask for a proof of acc ownership.
@Rikafip is right here. we can’t just accuse people and ask them to defend themselves. You pointed out some suspicious facts about user @simantobd but without real proof, these are still suspicious facts. He is an account reseller, it doesn't matter if it's a forum or an exchange account.
Max what you can do is to leave them a neutral tag to warn other members about account reseller and suspicious account activity.
btw. Facebook and Twitter account does not prove too much, it's very easy to change the username there and you can't be sure who's behind it.