Does you agree me to delete this giveaway if key does not work binding?

Yes. After a giveaway has ended you need the winners permission to delete the giveaway.

If the key is region locked/no longer valid, etc. you need the winner to agree to delete the giveaway, otherwise you have to accept non-received or provide a replacement.

If someone writes "you should agree to delete the giveaway..." this is not binding. It is a request, nothing more. If the winner does not agree to the deletion, there is no deletion.

You can't just delete one of your giveaways when it already has a winner. You always need the agreement of the giveaway winner (preferably posted in the giveaway so support can see this) to delete a giveaway after it has ended.

No. It doesn't change anything officially, and they still need your permission to delete.

It's more of an etiquette thing where the person isn't 100 % sure about the key, but has a decent enough reason to believe it works and still wants to do something nice by giving it away. They're trying to clarify that chance exists and leave it up to you whether you want to enter knowing that (and hopefully encourage you to be decent if it doesn't work since you're aware and "agreeing,' even if non-binding).

Whether you actually agree to delete the giveaway or not is still entirely up to you. Though--in most cases--you're probably being a real jerk if you demand the key instead of agreeing to delete since they did try to warn you and their intentions were good.

Well... unless they slap that sort of warning on every giveaway. In that case, they're the jerkass for trying to use it like some sort of legal protection freeing them from the same rules everyone else plays by just in case any key doesn't work when we all face that risk.

The manners part is just discretion and context. The rules are always the same though: its up to the winner.

all that stuff can be fixed if Steam makes the redeeming procedure in 2 steps(1: check the key, 2: activate the key-confirm activation))
just like what Sony did for Playstation

Your poll question is misleading.
You ask whether the statement is binding. It isn't.
But your poll just says 'Does it work?' which will lead a lot of people to answer differently. It might still work, it's still not binding.

The borked English is quite funny. . .hoping it's intentional.

Make a private (Invite Only) giveaway, make a thread about it and say that you give the GA link to everyone who agrees to delete the giveaway if the key is a duplicate.

People should read more, if you create a giveaway saying something and they don't read, the problem should be on the winner side, not the giveaway creator.
I've had to get the permissions to delete a giveaway 3 times because people can't read.

People will never forgive you, EVER. I always watch out and try to remember what keys I used, what I gave to to others, e.t.c. People will NEVER forgive you. Especially the giveaways that say "no not sent gifts".

I made a stupid thread regarding my worriness about it, and guess what? People called out I'm an idiot. So don't be stupid as well.

disgusting behavior by giveaway creators, nothing more.