Just a small correction, if you don't mind. Admins/mods do moderate spam and they delete spam posts as soon as they get reported. But you are correct when it comes to scams. Scam posts do not get deleted and scammers do not get banned. Dealing with scammers is left to dt members and the trust system.
But shouldn't the admins/mods get in the way when it's definitely a verified scammer? I think that banning scammers would help a lot in discouraging that behavior in the forum plus it will be a war of attrition from then on between admins banning scammers and scammers getting craftier until they get tired of scamming, I do hope that the kind of system where every DT is in agreement that someone is a scammer and that they should get the ban hammer.
The forum's decentralized DT work independantly based on their own judgment, not some central authority. If somebody provides convincing evidence against a supposed scammer, enough Decentralized Thinkers will slap a warning label on them and that red flag should clue in other users something fishy's going on. But the DT crew doesn't have banning power - they can only tag questionable characters.
The volunteer mods just enforce the basic rules - no spam/hate speech, etc and they usually can't verify fraud and scam claims. It's a judgement call and mods dont wanna overstep since members are so autonomous here.