DT name does not correspond essentially and almost nothing to do with trust.
Maybe not with trust in them in a monetarian way, but certainly with trust in their opinion/decissions and the feedbacks they give.
Basically if I can't trust those (or part of those) users with my money.. .. then I can't 100% trust their decision and feedbacks.
It's not so much about 100% trusting "their" feedback. If the trust rating is factual, with a proper reference (i.e. verifiable) you just need to decide if you agree with "their" reasoning and if the presented facts merit the big red warning.
I probably wouldn't trust 80% of my trust network with any non-dust amounts of money since I have no good way to determine what's their threshold for scamming. But I'm fine with the trust ratings they're posting thus they're in my trust network.
You do need to trust those in your trust network to a certain extent. Those who are in your trust network can also give positive ratings which will increase the trust score of others. There are a lot of trades that happen without a thread ever being created, so the plausibility of a positive rating without a reference is very high. If someone were to stay under the radar, not many people will notice when someone starts giving positive ratings when they might not be appropriate.
One example is master-P, as he generally did not piss anyone off, so people were not scrietizing his trust ratings, and he was able to give positive ratings to a number of his alts.
DT - or ideally the trust tree customized to everyone's preferences - is just a shortcut to separate the wheat from the chaff but it's not a replacement for due diligence. I can make my network tiny and include only people I trust but that wouldn't be very useful. I prefer a larger network of people whose criteria of evaluating others seems reasonable to me. That doesn't mean I'd trade blindly with anyone who's green on my screen and I wish newbies were somehow forced to learn that lesson before they post or PM in this forum.
There is always going to be a long con possibility in any system if that's what you're getting at, and yes, sometimes a prick like Master-P will sell out for 10 BTC. I think this specific type of escrow scam could have happened with or without a trust system and/or DT.
