In Agile Project Management the level of quality should be defined at the start of the project. And all work should aim to deliver that level of quality no more no less. If the business agrees that the features defined and the minimum usable subset has been provided adequately, then the solution should be acceptable. Unlike traditional projects quality should not become a variable, it is fixed at the outset. The design and testing are driven by the quality required and documentation should be appropriate to the quality needs. Tests are written before the deliverable is produced.
So all parties are aware of what the quality requirements are. And this also enables test to be undertaken early and frequently throughout development. Early and ongoing testing helps ensure the quality of the evolving solution. nasty surprises should not occur on time delivery is considered part of the quality acceptance for the project. Initial Moscow prioritization of the work and continual reassessment of what can be achieved within a time box ensures that time box is finished on time, every time