If you are not a developer, how can you test someone who is? I think you just need to bite the bullet and trust that person. If he’s good, he can provide you with questions for future hires.
Ask them which scripting language they use, and why. A good developer should be able to tell you that they use C#, and give a couple of reasons for it. But if pressed they should also be completely happy to work in UnityScript.
You’ll also want someone who has experiance programming outside of Unity. By the sounds of it you’ll want them to be able to do tech support in other areas too. Ask about web develpment, Xcode and the like.
Alternatively you could use a recruitment agency that specialises in hiring professionals and programmers in particular. Their fee will be far cheaper then cleanup if you get a dud programmer.
A good programmer should be able to work you through heir work step by step. They should be able to tell you what everything does, and how and why. Thy should show you code and explain the purpose of each line. If they can’t explain it in terms you understand they probably don’t have a strong understanding themselves.
They should also be familiar with buzz words, like OOP, design patterns and component based architecture.
Or I you have a ton of money to relocate someone you could hire me. I’m looking for a change of pace.
This thread is fascinating. In any hiring situation, you would ask questions to determine if the person you’re looking to hire fits the needs of your company. What you’re basically asking us is “What do we need?”
Why do you need a senior Unity developer? Why do you need a Unity developer at all? Do you have current orphan Unity projects that need finished? Is the role filling a vacancy or a new position? What skills are currently on the team and what skills are you lacking? These are all general hiring questions that are good to know before you even post a listing.