I've never gambled on tf2 mostly because I know there's better places for gambling on games anyways.
Runescape is perfect if you have a maxed account because you can get true 50/50 odds on boxing, and the money is easier to turn into cash because there's a much bigger market and it's extremely easy to get any items right into sell-able gold.
I'm trying to not gambling at all though, I can never stop myself to actually make a profit.