*Isn't this solved by paying a fixed amount, and only paying if the project work...

Isn't this solved by paying a fixed amount, and only paying if the project works and is well done?

The problem with that approach is metrics. How can to specify that the softwere "works"? How can you measure if it's "well done"?

I worked on a project using that approach and most of the time was spent being basically lawyers with specs instead of contracts. Horrible experience.