Indie games keys: what if there's a mistake?

There's no non-destructive way to tell if a key is still unactivated.

No, you can't giveaway the key / make a giveaway if the key isn't going to activate 100% successfully.

Also, just ask your friends / look through their profiles and see which games from the bundle have been redeemed (i.e. the friend owns the game) and then cross those keys off -> gift the ones not left?

Dump the keys in the forums and screw the contributor value?

Some people have mentioned that Steam Support can verify the keys have or haven't been used but I'm not sure if thats a myth or not.

Better Way to giveaway at forum so if you found any game not active you can giveaway another

Do the giveaway during the winter sale so if the key doesn't work, you can just buy a copy of the game.

if you send me the keys i can check them for you ;)

Well you can`t really do that. If you want to giveaway them on this site, I think the only option is to post them on this topic.

There is no way to do this on your own.

I have read about other users that claimed, that they contacted Steam support and had them check if the key was already used.

1. You can proof a key by giving it to one who already has the game and let him activate it to see what game it is (the key will not be used). But I'm not 100% sure that that works.

2. You can't make a giveaway for another game that you want to give away but you could make a giveaway for a cheap game (e.g. Fortix) and give the winner as extra to Fortix the other game.

Edit: 1. does not work, but you can do the second option. Thanks Dopefish.