Ask them:

How do they ensure that the code they deliver to their teammates is of high quality?

Regardless of domain, the principles are the same -- answers that can be understood even by a non-technical person include "peer review of my work" and "assume good faith when a person provides feedback on your design and results". If you do have a technical background, then the technical answers provided should apply to all types of software development and technical operations. You don't need to specifically have iOS experience.