Deferred Value
This is a type of project where a cost isn’t determined upfront. Upon the completion of a project, the client will pay you what they think the project is worth. While this structure highlights the need to take into account the value received by the client, it’s very one-sided. It also only takes into account the final product — the work delivered — and excludes your guidance in steering towards this goal.
I would advise that no one ever agree to this structure.