The only way to ensure positive results is to use an escrow service, which you can find in the Marketplace here at RCU. Otherwise there is no guarantee. Aside from that it helps to get as much information about the person as possible, verify the information as accurate, call the person on the phone and get to know them a little better, etc. Judge them by their responses to your emails and how quickly they respond. Ask for current pictures with the vehicle in a shot of your choosing so you know it's current. Basically, use your head. There is no guarantee even still, but it does help secure a positive result to your trade.