Yes, but those are smaller than the converse, where the conversation is about whether something ambiguous/new is in or out of scope (strictly adversarial discussion), rather than whether such ambiguous items are worth it or not to the client (simply a resource allocation discussion).
I have a hard time believing that the potential conflict of interest situation that emerges from a fixed-price engagement, where the customer ultimately can accept or reject the work, would be worse than the elemental conflict of interest that emerges from hourly billing, where customers have little control or even insight into hours billed.
