If I’m correct this transaction just took place in less down two hours ago, the users might appear to be online but might actually not be active on the forum, since he have not made any post since after the transaction,

to me I will say you should give him little more time to see if it’s a scam or not for now I will say you are too quick to call him a scammer, the deal was done public as I can see the thread the accused users opened, and I don’t think any DT will be in a rush to tag an account for that until the accused prove that he’s indeed a scammer.