1. System will check whether both of them have replied in the respective thread. For example, I have created a thread in marketplace for buying something. You as a NON-DT member can only provide feedback if you have replied in that thread.
This just wouldn't work unfortunately. The scammer could easily delete his posts, and then the system fails. Or post a scam thread and immediately lock it - then no one can post in the thread and therefore no one could leave feedback.
2. If a scammer don't create a thread even, or don't make a reply in any thread, how will we even know that he is scammer. Also, DT can provide feedback. And the link will verify the proof.
Many scammers try to avoid detection and tagging by sending their scams out in PMs only. Then there are no posts
and no links for verification.
I don't mean to be discouraging here, but there are just too many holes in this system for it to work.