I think that its fairly obvious if your getting done,
I recieved these two PM's last week, needless to say, I didnt take the offer!
There is not alot that can really be done to stop this happening, BUT as has been mentioned, if you stick to the rules (IE: dont carry out a sale through PM) then you're safe! Its pretty clear that this guy was full of bull, at the time he messaged me, he had 1 post!