Re: build and sell
Unfortuatly, "Hold Harmless" Agreements are not much protection at all. Ask any lawyer. If there's money in it for them, they will eagerly fight it in court.. Especialy if someone becomes permanantly incapacitated or dies on something that you built. There's no protection at all to keep the family from suing.
I used to be an Ultralight instructor, and after dealing with a few crazy students, I decided that I was exposing myself and my estate to too much liability risk.