Giveaways with gamekeys you are not sure if they work

You should make a giveaway for a key that you know will work. A giveaway winner is entitled to a copy of the game they won and you are responsible to get them a working key.

EDIT If you have several keys for the same game add them on steam and have them try a couple if the first one didn't work. Just say in the giveaway description "I have several keys for this and I'm not sure which one has not been used accept my friend request if you win"

A "not received" giveaway will take away one of your giveaway slots, and probably get you a blacklist from someone.

We have a thread for keys that you aren't sure have been redeemed, maybe just drop it there for science? Here

If you get too many not received, you'll get suspended. Giveaway, once it is finished, will only be deleted if the winner agrees to.

http://www.steamgifts.com/discussion/MYeOi/orphan-keys-drop-thread

The trick is, do the giveaway for a closed group that you can trust.
So long as the winner is willing to say "I agree to cancel", staff will simply delete the giveaway [you lose the one giveaway slot either way, of course, but there's no mark on your account].

As far as punishment, staff told me that there's not necessarily any direct punishment for it (you may get a brief suspension, depending on circumstances) but if they notice a pattern they'll consider it abuse of the site and respond accordingly.
tl;dr version, if you say in the description it's a potentially invalid key, and it's a rare occurrence, you ought be fine.

Of course, doing the first one is your best bet- whether my error, GMG occasionally invalidating keys past the first week, IG locking me out of my account, or so forth, people've consistently been fine with agreeing to cancel for me. Likewise, I've returned the courtesy several times as well.

Basically, anyone that enters a giveaway where you note such a possibility, and then is unwilling to do the cancellation they agreed to on entry, is a massive, selfish, entitled ass attempting to coerce you into giving them a game.
Of course, in my cases, I didn't know of the possibilities, and people covered me on it regardless.
So I reemphasize: Just send the giveaway to individuals you trust to respond appropriately.

A good approach is to use a group that'd kick members if the violated that sort of agreement, as then there's a safety net.
When in doubt, make your own group [or if you're confident in it, use your whitelist]!

P.S. The Orphan Keys thread is a hot mess that you should only ever throw keys you absolutely hate toward.
Groups often have key-drop threads, and you can always create a thread to select someone to give to, directly.
While a bit different in scope, http://www.steamgifts.com/discussion/EKaPm/ is a good example of reliably getting non-giveaway-able keys to individuals.