That would presumably be treated the same as a human CSA doing the same thing.
A human CSA can give you a discount, and that is usually binding. They can't declare X corp is going to mail a box of donuts to you every day for the rest of your life and have it be.
So my expectation would be (in the absence of real world cases currently) that if you negotiate the AI into giving you a 10% discount on your bill.. it would be binding typically.
Now if there's prompt hacking involved or obvious attempts to trick the AI, that would not be binding.
A judge will not look favorably on your 5000 token prompt of carefully selected instructions telling the AI to go wild
But one day maybe even the judge will be an AI...