Always check their profile before dealing with them. Make sure they are not imposter and the profile must match with inventory. If they have ban record then just cancel the deal because they most likely are scammer.
Another important thing is dont trade the game first unless the buyer have many good reputation and positive feedbacks on their profile page. That is why middleman exist in tf2 to handle game/cash trade. Some example of rep are in my profile page http://steamcommunity.com/id/MrBeanster .
Steam Profile reps are useless since the profile owner can always delete the bad remarks, like what me & another LYN member experienced with a certain Singaporean.