amok: also - there is a lot more people (even though most of them do not trade much) who just take an advantage of a trade now and then when it fits them - how do they get on the list? and would not this list become much larger then the others? Is the baseline that everyone not on the list a scammer?
Well it's only like having a security certificate for a website or, I suppose more accurately, a rating on eBay. On eBay, a person with a low rating isn't necessarily untrustworthy but you do accept that dealing with him is potentially more of a risk. Just letting people make informed decisions. If two people who aren't "trusted" want to trade, you could potentially use a trusted person to hold both codes, then give them to the other side of the two traders, if you see what I mean.
The problem with an untrusted list is that (a) it will keep growing meaninglessly as scammers change their name and (b) people will only get added to it after they scam someone, so there'll always be at least one victim. With a trusted list, it's just saying "Hey, these guys are cool, and they can also be the middleman in a trade you might want to do with a new user". The list won't grow that much since it'll mainly consist of the more longterm GOG users and only people who are interested in being part of the process.
Anyway, small elite groups aren't created, they're simply discovered. ;)