Telika: Say, as I don't trade, I'm not following this attentively, or caring immensely, so, i certainly missed something mmensely obvious, but... i didn't get how a general politeness rule of "lowest rep gives key first" can't solve most of the issues ?
The only problem with this is that when somebody contacts you via PM, there appears to be no way to search for them on the forums, and therefore there is no way to discern their reputation or whether they are a reliable member of the community :(.
Unfortunately, I don't know everybody on the forums, and I only became regularly active a fairly short time ago. When people contact me via PM, I have no choice but to trust them unless they exhibit strange behaviour (or my inexplicable sixth sense warns me).
The only real solution I see to this is to trade only with people you know/have talked to on the forums, or ask the person you are trading with to link you to a thread where they have posted so that you can find out more about them. Unfortunately, this puts new users at a significant disadvantage. From now on, I'll ask people to send me their keys first, unless I know that they are trustworthy. At least I have people who can vouch for me in the trading thread.
This whole incident with the scammer(s) makes me sad, but I suppose it was bound to happen eventually. I just hope whoever he/she/they are will get bored eventually and move on to another community (although I don't wish them on any decent community).