state who it is and get some feedback from other members if possible, look back at his posts and see if he is a decent bloke or an ass.

Make sure you get a name and address to send the cheque recorded delivery to, so that if he fails to deliver, you can go and get your money back, and pay for recorded delivery or even better organise your own courier to collect.

always a risk but if they are a regular user, and you have a correct address and traceable couries then you limit the chances.