I did the prepare for preorder on ATT site. The 12 ProMax I am upgrading has a cracked back screen which I noted when going through the Q&A. The normal trade in value would have been $260 - but that was crossed out and it said $1000. So ATT offering a hefty bonus for first day orders it seems - never seen this before. Can't imagine it working like this on the Apple site.
Question #3 on A&T's site is tricky... Is says "Is the screen and device functioning correctly, free of chips, cracks, major brusing/burn-in and less than three missing pixels?" and then proceeds with subbullets only related to the screen (seemingly). I believe the correct answer to #3 (if you have a cracked back) is actually going to be NO, which brings the value of the 12 Pro Max down to $130 (so just barely in the $830 credit tier).
I am in the same boat as you and will be pleasantly surprised if they offer me $1000, but after looking around at various sources I am only expecting $830 credit (still a great value for a cracked phone imo).
The problem is, you cannot get any of this to show up if you do the pre-pre-order through Apple. As soon as you answer that the device has cracks, it defaults to "Apple will recycle it for you", and you can't even get carrier trade-in offer values to pop up like others have shown.
My plan, again, is to pre-pre-order through Apple by stating "no Trade-in" and "Carrier Financing" through AT&T, and then bringing it into AT&T to get my credits after my new phone is delivered. I've read through AT&T's terms and conditions, and don't see any that I'm violating with this approach, it just says you have to trade-in a device on the list within 30 days...