[open-source-ux]

A possible idea: one price with a fixed number of revisions. For additional revisions, you offer an add-on option i.e. the client can purchase additional revisions for a fee you set.

As other posters have said, offering unlimited designs might give some customers unreasonable or demanding expectations. Will an 'unlimited' option swamp you with revision requests?

Another suggestion: make your work a more prominent showcase on your website. Potential customers what to see examples of your app designs and user stories. Your current designs don't have any context - they are simply mockups (good-looking mockups) with no description. Do they need more detail and context? A case study for example. Make it clear to customers what they can get from your service - show off you work in the best possible light to catch their interest. Good luck :-)