This situation is a bit confusing. From your summary, it sounds like you have an idea and product you are building and you need some help with sales. It sounds like you only have a prototype at this stage. It feels very early to me to join an existing company with a prototype just for their sales consulting. Is there a reason that you won't hire this company as a freelancer first and then maybe consider a partnership if it works out?
What does this other company do? Is it just sales consulting? Or do they have a product?
What does this other company do? Is it just sales consulting? Or do they have a product?