(let's say) I red trusted this guy for example but there is a problem.
https://bitcointalk.org/index.php?action=profile;u=167659How do I know If this isn't a game to make these accounts get red trust?
The account is suspicious as fuck with no merits, only 2 posts in 2018. But how can I be sure?
1. I was speaking to an account seller
2. He offered to sell this account
3. He proved that he indeed owns this account.
I understand this concern regarding the other accounts (where i didn't get any proof about the ownership)
I mean.. i could say "i sell account 'theymos' for 1 BTC'.. without proof you can't be sure.
But in this case i strongly believe this is evidence enough

What exact scenario are you insecure about ? How can this be a game if the owner of the account took part in it ?