Preventing (some) regifters and idea

and I am sure it can't check if a key was already given away or not
unless CG pays Archi for it to do so

You don't understand how key checking works, at all.

You can't simply check if key is used or not. Checking code automatically redeems it, unless you have it already, in this case you will get AlreadyOwned message, which tells absolutely nothing about whether key is used or not - only if it's valid.

And if you don't own the game, then it will automatically redeem the key, or state that it's duplicated if it has been used already.

On top of all of that you're limited to something like 20 failed key tries per hour, and you can't go above that. Everything is failed key try, apart from successfully redeeming the key.

So no, you can't use ASF, ArchiBoT, neither any custom code to "check" keys. You can only attempt to redeem them, and get message in return - nothing more, nothing less. I can't imagine how you would implement it into SG - it doesn't make any sense.

And what you truly want to implement, has been suggested already.