I do agree that I sent him a message to buy what he was trying to sell and notice that his account was not in a good condition so turn down that sale.
If it were in good condition you would have bought it, this is not excuse.
Do you have proof that this account belongs to him? This is not valid proof.
And what this has to do with this topic?
The same goes for you, do you have proofs that his account has been hacked? You can't accuse someone just because he has changed password or email.