The other thing to think about is that even though it may be your best friend or your brother, what happens when they trade away an item that YOU loved, but they didn't. You log on and it's gone. OTM isn't gonna do squat about it because as far as they're aware, it was YOU that traded it, not your friend or brother. It's still beyond me that people share accounts...They may be your "friend" or blood relative... but greed and pixels aren't a good mix and bad things happen.
+1 I saw a person get scammed by their brother when he shared his account info. Another person I know got scammed by his cousin when his info was shared. In both cases the relative stole stuff from their account, and sold off expensive items.