Always, Always! Click their Steamtrade profile and follow that to their actual steam profile (their name in blue links to steamtrades and steam profile) If someone randomly add's you out of the blue without posting on your thread, Demand! they post on your thread so you can check their info. Too many people pulling this impersonation scam and too many people are falling for it. We terribly need a sticky for info like this and steam accounts to watch out for. One huge rule (posted up top as well) NEVER trade with a private profile.
http://steamcommunity.com/profiles/76561198052817822
http://steamcommunity.com/id/HKGdot
http://steamcommunity.com/profiles/76561198054414811
http://steamcommunity.com/id/_vacsek
http://steamcommunity.com/profiles/76561198077997006
Other people to watch out for (most of them Also impersonate well known and newer traders.)
Please be sure to check profiles of people you trade with, someone (linked below) is impersonating me, never trade with people who have their account set to private and always make sure that their steam profile matches the profile from steamtrades.com
http://steamcommunity.com/profiles/76561197979031870
Also run their profile through steamrep.In this case, the user had been reported and confirmed 4 times.
http://www.steamrep.com/