Well it sounds like your system would be a good trade feedback system. Although it would not do anything to prevent scams from happening in the first place. For example if a user is offering a too good to be true offer then how is an unexperienced user suppose to know that it is probably a scam? I know that tomatocage often screens people's actual willingness to accept escrow with newbie accounts and flags them with his own account when they show signs of not accepting escrow (e.g. they stop responding). What about people who make statements that they are desperate for money then all of a sudden start to sell something very expensive? What about face-to-face deals and other deals not done within the forum?
Again, the bolded.
Too good to be true offers are received by everyone with email on a periodic basis - advance fee fraud. And in postal mail - other types of fraud. And via the phone. And everyone behind a door that strangers can easily get to, who parks their vehicle in public, or who can communicate with any other human being in any fashion whatsoever. If you don't go through life with the mindset of "trust no one, verify everyone", you will get scammed.
Nothing can
prevent scams (on bitcointalk)
from happening in the first place other than pre-post/pre-edit moderating all contact methods out of posts and eliminating the private message system, links to instant messengers, etc.
The most favorable description of default trust is "the good" - but logically, you cannot simultaneously have "the perfect" you described in bold: the good but flawed system is mutually exclusive of the perfect system.
It seems that those who illogically defend default trust the most, while hypocritically making "the perfect" the enemy of their "good", must be the ones who come up with
a better system...idea
that ACTUALLY
prevent(s) scams from happening in the first place.
ETA: Let's draw an analogy, though I'm not a master at it: you are stranded on a desert island with a laptop, satellite internet, and a cup, but do not call for rescue. You scoop up seawater with your cup and drink it. You do not drink any other water or liquid. You post on the internet that you're feeling worse by the day, describing your symptoms. People ask "what are you drinking?" - you tell them only unprocessed seawater. People tell you that you can't do that without eventually killing yourself. You tell them "but there's all the water I'd ever need to drink right here from the ocean! Screw you guys!" and throw your laptop into the ocean. Rather than heading inland to search for fresh water, moisture-rich foods, you die of extreme salt intake.
Economic suicide is happening everywhere, irrespective of "good" systems. At least TRY to be perfect, even if it's rarely possible to be.