TF2 + CS:GO Keys Gifting

yes it is

You can trade tf2 or csgo keys for humble bundle keys, buy you can easily get scammed, becouse somebody has to give the game key or the csgo keys first.

Example:

1. You give your tf2/csgo keys first via trade window
2. You will get the HB key (or you dont get anything cos you got scammed)

There is no safe way to trade for game keys.

It's ok, of course if trader have a high and good rep (but with your profile and low rep you must go first).