Auto-ban who ? If DT gives you 2 negative (for example) you are not able to send PM to newbies ? (sorry if I misunderstood)
Trust: +0 / =0 / -0 ratings do appear in PMs, so there's that at least
And also would assume most of the scams happen outside the forum, like Telegram etc.

Nothing is automatic here. Bans, locked accounts, reports, feedback, DT etc they all have human intervention in one form or another. I guess besides profile settings "ignore newbie PM" and "ignore user posts/pm" , but you get the idea. I doubt the first "automation" would involve something serious like bans, be it only for PMs.