The stupidity of the LLM is completely irrelevant. If you hired a salesperson to negotiate deals, and they offer a massive discount to a customer that you wouldn't normally approve, you're still liable for that discount. If you're dumb enough to let a bot that you cannot control negotiate with customers for you, you are liable for what it agrees to so long as it is within the apparent authority. That is, the salesperson bot does not have apparent authority to sell company equity, for example.