Ditto is designed to minimize the risks associated with project-based work. If you're concerned that a project may not work out, we recommend keeping the phases small. This reduces the amount of money on the line at any given time and keeps feedback loops tight.
That being said, if both client and contractor agree that a refund is in order, we're happy to help make that happen. Note that this must be a mutual request, as outlined in the Ditto Master Services Agreement (part of the Ditto Terms & Conditions).
Please reach out via support channels for assistance.