If they are true sales guys, they won't be offended with having their take away being results based. Risk and reward after all. Your friend has already created

If they are true sales guys, they won't be offended with having their take away being results based. Risk and reward after all. Your friend has already created the product and taken the risk, the sales guys now need to shoulder that risk. My opinion: work out something that forgoes ownership until results are evident. Perhaps a profit sharing plan, or even a patent on the device that he could retain ownership to for a set period of time. I'm not sure of the legality of this, so your friend should talk to a lawyer, but that's what my take would be.