Yup, I understand what you're saying. This site does put a lot of responsibilitty on the shoulders of giveaway creators. But with good reasons; the result of it being >99,9% of all giveaways actually being delivered. That's crucial for a gifting community. In my experience winners generally understand and agree to deletion if there's something wrong with a key escpecially if you warn them beforehand. You could phrase it something like this: "If the key turns out to be invalid I'd appreciate it if you'd let me delete the giveaway."

You just cannot make a rule out of it, because why would this rule be acceptable and others (you must write a poem for me like my instagram post, click this referral link, vote person x and proof it etc etc) not... It's a slippery slope...

I've given away >2000 games/keys and I think I've had problems with faulty keys only once or twice. It was not difficult at all to talk to the winners about it. And even if they wouldn't agree to delete the giveaway, they simply would mark the game as not recieved. That would not be the end of the world, right?