I think a large amount of our FATs for engineered pumps will run into 'problems', but ones that are easily ameliorated physically. If they can't be, they will try to convince the customer its okay, even when it may not be okay. If either the customer is conifdent enough to insist, or if they are ignorant enough to not understand why the factory test is not equivalent to the field setup, then I come in and try to convince them, or less often, try to fix the problem.
Of all pumps, disputes (any diagreement that warrants further testing or modifications to the test setup or machine) I'd guess at about 5%. For disputes that last longer than a few days, maybe 1%. If all witnesses were vibration experts, I suspect this would be 5x higher.