What do you guys think of steam key selling sites like G2A, Instant-Gaming etc.?

[raremens]

I buy old games there sometimes because of the huge discounts but I know the keys aren't legit.

[fenrif]

I think they're great.

[Mario]

Avoiding them like the plague. Not talking about authorized sellers like Humble Bundle or Green Man Gaming though.

The keys aren't necessarily illegal or non-legit, but chances aren't too low and/or there's at least some kind of sketchy thing involved (even if it's just "importing" cheap Asian or Russian keys).