My question here is:
1. Are scammers really welcomed in the forum to stay for long.
Answer to this is obvious and not even tolerated for long having some evidence and proof that he did scammed or planning a scam activity like this.
2. Other than having a RT (red trust) as a penalty, is there no other ways this scammers issues can be addressed for them not to return to the forum again.
If the person have red tagged already then everyone will be alerted not make any transaction or deal. Scammer as @Jawhead999 mentioned arent not moderated but you can always report to moderator any sort of activity he does that sound suspicious.
He is indeed using Bounty Detective format on Bounty, Im not sure if this can be flagged as plagiarism more likely not.