How to negotiate for know-how or advice

in the past month I've been formulating a new startup idea in my head. It's not something technologically advanced that can't be made by me and my team but it belongs in the health industry and I will definitely need a physician trained on the subject to help me along from start, to testing, to launch. Maybe more than one.

My question is what's the proper way to approach someone and align him with the interests of the project? Obviously he needs strong motives to help, so is it reasonable to give equity? How much do you think would be worth the effort?

The best motivation is to find someone who needs it/wants it for them to do their job better or have a competitive advantage.

You get someone who will also use the product, promote it and give valuable feedback in testing and usability. You won't have that with someone who is just giving you professional advice or scientific opinions.

Don't make the mistake of looking for someone to motivate or "align" with equity.

Find someone passionate about the solution/field.

I was involved in a similar startup a while back...

We have a slight advantage though, the person with the idea had worked as a nurse&midwife and her husband was a doctor so there were some personal connections to be used. So there was a product idea that was rather complete but needed to bee tested out and see if it was designed correctly and if the features was correct.

So we were only in need of staff to test the product & UI on, the domain knowledge we had before hand.

We were able to use all sorts of personal contacts and the local university that educates nurses to find both pre-grad nurses, nurses and doctors to test with. Also since we were doing a safety product we got in touch with the head of the hospital and they liked it and gave us an opportunity to test it on a department.

The "only" thing we gave the persons we tested it out on was a thanks for there time, they got to see the product as it could be, was able to contribute to the work flow, and small things like checks to go see a movie. As for the hospital there was an option to get the final product at a discount for a period as a thanks for the help.