For me a good developer is someone that will deliver a mobile app that achieves your goals. That means :
- he can help you to define/refine your goals with mookups, iterative and agile developments, you should take a little time to understand what your role as "product owner" is (http://www.romanpichler.com/blog/one-page-product-owner/)
- he will deliver the mobile app on the app store : he has already done that, he is aware of what is possible or not according to Apple's rules, ask him to show you working examples of available apps, did he deploy on all iOS versions or on iOS7 only, which model of iPhone/iPad does he have for his tests ....
- he can give you some advices if you need to deliver your app on another mobile platform (Android at least, WindowsPhone) because Apple does not catch all the market, if you really need a native app or if you can deal with a web app.
You can also book a pair programmer to review his code during the iterations, check the QA (quality assurance) and test the app as a user, have a look at www.airpair.com.
Don't hesitate to have a call with an expert on Clarity if you need help.