The only way you are assured a proper deal is to use escrow.... anyone selling equipment without escrow available is more than likely a scam. If it is a self moderated topic as well.... another HUGE red flag. All buyers beware of sellers that state NO ESCROW in the OP or do not accept it at any point.
Indeed any seller refusing to accept escrow should be avoided, I have avoided many sellers who were not keen on using escrow. Then one thing you should remember choose a trustworthy escrow, I recommend Ognasty though there're others too you could consider. This is often ignored by all check if the account password has been recently reset, that would mean someone else has brought it then insist on a signed messsge. Lastly go to sellers profile then click on trust and show ratings see if he has any red before making any deal.