As I mentioned in the last post, your publisher will have pretty much unfettered discretion to determine whether to accept or reject your manuscript. Unless you put in some criteria to govern the decision.
Much though your publisher might not want you to know it, there are ways to do this that can give you some assistance in the event that your publisher tries to reject and take away the fee that you would be paid on acceptance. There's as many ways to do this as there are to write down words in a contract, but here's four methods that have been used in reported cases or in contracts that I've seen.
1. Compare it to one of your previous works: the manuscript is acceptable if it is "equivalent in quality to the author's previous book" or "any of the author's three previous books" or any other work that you yourself have produced. This may not be the best idea for your second book - no sense tempting the fates (or the sophomore jinx) - but if you've got a few books under your belt then it might work to your benefit.
2. Compare it to the outline and sample chapters: the manuscript is acceptable if it is "an accurate" or "a faithful embodiment of the outline and sample chapters." This is a bit less subjective than some of the other tests so might be a good choice for a second or even first book.
3. For a biography or other profile of a third party, you can rely on the third party: the manuscript is acceptable if the subject approves its content. One place to push for something like this is in a ghostwriter or celebrity bio contract, where there's a danger the publisher will treat you like a commodity who can be replaced. This way they can't job the project out to multiple people and reject your manuscript just because they like someone else's better.
4. Even where there's no obvious third party, you can still try to get this: a neutral third party reviews it and decides whether the publisher was justified in rejecting. This will be expensive, but if you're willing to charge the cost against your acceptance fee it might make things a bit more palatable.
Yes, at the end of the day these are all subjective. But if your acceptance fee is hanging in the balance, you might want to have something to point to when claiming your publisher isn't abiding by their side of the deal.