If you add me and your account looks suspicious I'm going to assume you're some sort of scambot and block you. If you're adding me to trade you are also out of luck since I'm not selling anything, so don't even bother.

If you're adding me cause you had fun playing with me in some sort of multiplayer game, or on the forums and want to be friends, feel free to add away. Just let me know first since I probably don't remember you. This is just a disclaimer since I so often get added by scammers and bots due to the value of my inventory.

Here is some of the behavior I find suspicious:
A low level account that hasn't played any games.
An account recently created.
Accounts that appear to be impersonating other more famous accounts (I do double check).
Someone with almost no hours in a game like tf2 or cs:go yet have all the achievements completed.
Accounts that are advertising some website on their main page.
Accounts that use wording that indicate they are most likely bots.