In a weird way, when it comes to home purchases you actually have to negotiate no negotiations. So in real life you can't actually accomplish what you want.

And if you want to go further and opt out of the standard home purchase contract entirely you get lawyers involved on both sides so you're again negotiating.

The implicit assumption you're making is that offering the house at 80/90% of market value is a concession but that's not how that works. You can't do the negotiation for the other side, say take it or leave it, and say that counts. You can't negotiate against an imagined person in advance

If you offer it take it or leave it you're at the whim of the judge saying, "that's absurd no reasonable person would assume that was in a home purchase contract."