screenshot all interactions- especially the trade transaction completion window(s). also if suspect - obviously don't blindly go first- but also avoid doing negotiations etc on psn chat. stick to doing all of your dealings on mut chat- I would even suggest not doing anything in PMs. Never hurts also be redundant and use your posts to force trader to commit- for example " I will post UT vick in trade and you will offer ut sanders - once I accept then I will post a auction for 100k selling San Fran Standium- You will buy. Are we in agreement? " or similar - all you need back is him to post "yes" and you can use his post to prove your case - if infact he neglects to follow through with his word.