We don't limit the number of times that a client can refuse to release payment. As far as Ditto is concerned, that is between the contractor and the client.
If there is a disagreement, we expect that you'll work together to resolve it in a timely manner. If you can't, and you find yourselves in a lengthy dispute, Ditto reserves the right to turn funds over to a court of law for resolution. (So basically - we're not getting in the middle of this!)
We assume positive intent and hope you do, too.
(All of this is outlined in "legalese" as part of the Ditto Terms & Conditions, which every user of Ditto must agree to in order to sign up and use Ditto.)