Instead of only displaying one number, be it positive or negative, you should show both the successful trades and the number of negative trades side by side. The principle being that its easy for 3-4 friends to pretend to have had positive trades to get into the positives, to lure in a potential seller and steal their items. However if you see for example WildSelv +4, -2 you'd see I have had 4 successful trades but 2 of them were not suggesting that the 4 successful trades were fake.