As it has been a while since you have done some giveaways, just FYI, you can't force the winner to automatically agree to deleting the giveaway. Staff has said only winner and support staff have any say in that matter.

Check this Public Service Announcement from last year:
https://www.steamgifts.com/discussion/5fkrA/

Best you can do is:

"Please allow me to delete the giveaway if the key doesn't work"

It´s on my wishlist.
Thank you and have a nice thursday.
The weekend is near ^^

Thank you!!

Have also some keys I don't know if they work. Thanks for the "surprise"-chance ;-)

thanks!