You did 2 trades with him to say you did 2 trades with him.
Why does it matter if you do 1 or 2 trades with him?
I know for a fact OS-scape has admins and mods that are given tonnes of BM to sell on places like here, then they are tracked, if they buy more they are let off the hook, but if they are selling that gold to other people, bam, they are banned, they also check the logs on the accounts and ban the people they sold too, so greedy but it's worked wonders for them.
I really doubt there was an admin checking logs every 5 minutes to see any potential RWTers + actual RWTers (not on sythe) are banned only with significant proof / has to be a thread about them, so if that all happened within 20-30 minutes that is just nearly impossible, they would of only have done it if there was absolute guarantee the guy was RWTing and wasn't just giving it away for example or won it dicing / gambling, so they must've somehow have known it was RWTed and not any of the above.
Also I bought 200k at around the same time, I was fine, so there is no system, it's done manually on the logs, which like I said, is so unlikely they monitor.