[TheFullStack]

The best way is to have a developer friend/colleague evaluate the candidate's skill on your behalf. Preferably someone who manages other devs or has had to hire devs previously. There is really no practical way you yourself can make the evaluation.

[afarrell]

How I imagine this going is that you have a developer friend who supports what you are doing but who isn’t at a place in her life where she can quit her job to focus on an early-stage startup. So y’all make an arrangement where you pay her to do interviews.

How should you structure the payment?

[TheFullStack]

Sounds about right. If the founder was a good friend of mine, I would just screen devs for free. If it was a friend-of-a-friend type situation, I would bill my normal hourly rate (I am a contractor).

[paulddraper]

This is the only practical solution. You can get a feel for soft-skills/likeability but when it comes to hard-skills, the phrase "it takes one to know one" applies.