Need Help Concerning SteamGifts

You can gift them, but you'll be responsible for as many keys as are included in the giveaway. So if you guess that five are valid, but only four are, you'll need to come up with another working key, or get "Not Received" feedback. Having such feedback will remove a giveaway slot, if I understand correctly, and if you get too many Not Received keys, you can get suspended I believe.

You can, but by creating a giveaway that ends and assigns a winner, you are technically committing yourself to giving that game to the recipient; if the key doesn't work, you have to get another copy.

In your case, people usually do one of two things:

1. Create an invite-only forum giveaway and only share its link with people who agree on deleting the giveaway if the key doesn't work. You will lose one of your initial 3 slots for each deleted one though, so 3 deleted giveaways = you cannot do more.
2. You dump them in the forum, your Steam activity feed, or keygiveaway.com. Even if they don't work, nothing is lost. But you won't get CV here for them.

Hello, simple answer is no :D

For I understand you have to guaranty to deliver the game.
But lately, some user do small giveaway for whitelist people he recrute on the forum the only thing is ask was to agree to delete the giveaway if the key was already use. I also will advise you to make one giveaway by key.
Have a nice day

Make a topic , explaining in detail that the keys may NOT work , add people who are willing to take the risk to your whitelist ( or make a group and share it with them there ) and state that if the key is not working , they accept that you can delete the giveaway .

Dont make invite only giveaway since someone may enter without reading the rules and refuse to let you delete the giveaway ... saw that happen once >.<

Not necessarily recommendable but certainly possible depending on the amount of available keys and only if you know how many of them are used.

Technically, if you know exactly how many are used (X) out of all of them (N), even if you don't know which ones, you could create N-X giveaways and have a spare key for each used one. You can add a margin of error by creating N-X-Y giveaways where Y is the amount of reserved keys you want to allocate just in case one of the working ones proves to be used as well.
By doing this you have to clearly specify in the giveaway description that in case the key doesn't work, you'll provide another one.