The first thing I recommend is determining what you want from the partnership, chat with the person and see what they want. Hire a business valuation person to see what they see as tangible and intangible assets of the company. Sit down with a lawyer and ask advice from experts. I was recently coaching a client with a similar issue (he was the one wanting to buy in) the owner felt his toilets were made of gold. This can be an emotional thing, use experts to take the emotion out of it.

If you want to chat more, give me a shout. I know some great experts.

Michael