I would suggest to stop mobbing and witch hunting (and complaining that scammers scammed the scammer).
If someone check the winner it can see that it's a legit user, but it's still true that he "stole " a key, i was in his position and banned those users so if you don't like "my giveaway" (my = users that uses non-stema keys) you won't be able to enter and stop.
I won a lot of giveaways with no-steam keys, i have never left a negative for a working one, if i was missing the game i took it, if i already had it i gifted it to other.
And, it's not a "wtich hunt", it's a matter of trust, i will immediatly ban an user that stole one of my key, no matter the reason, no matther his level and how many giveaway he make, i will be probably banned back but for me will be a matter of principle.
Lastly i don't see UltraInstinct as a cammer, most of the people here only want to get free games, ANY free games, and they go against "site limitations" to do so, if you think that those people are all scammers, well, for me you're at fault.