Approached About Partnership

I am a software developer and for the past 4-5 years I've worked part-time on an application related to fantasy sports. I enjoy toying with the marketing side of things but I focus mainly on writing code and improving the functionality of the application. My application is completely free but I do make money off advertisements and affiliate sales. The idea is down the line I will charge a small fee for 'premium features', but that a free version will always be available.

I was recently contacted by someone who is a sales/marketing specialist. They are proposing to form a partnership where they would promote/market the site and I would focus on the coding side. This person has offered to use his own money to finance the marketing of the website in exchange for a partial ownership of the company. I've never considered a partner so I'm in uncharted waters here.

Because I've already put in 4-5 years of sweat-equity into this business it would be very difficult for me to give up any ownership in the short-term. I could definitely use the help promoting the site, and would be more than willing to pay this person for their efforts, but I'm not sure what would constitute a fair deal at this point. Because my site is free at this point, there is no money to pay a salary so compensation would have to be based on a percentage of profits.

My traffic/income has grown steadily over these 5 years without much marketing; usually doubling each year and last year by around 300%. We're not talking big-bucks here, but I have total belief that with the right promotion and continued development the sky is the limit. For the longest time this has just been a hobby site for me, but the new guy believes it has much higher potential.

Some of my questions are:

1. Should considering a partnership even be an option at this point? I believe it is way too early to even think about since I barely know this person, but even if trust was built how would they ever make up for my 5 years of sweat-equity? I don't know how to quantify that.
2. If I choose to simply pay this guy a percentage of the profits for his promotional/marketing work, what is a fair number? If I theoretically made $2000 last year, would I only pay him a percentage of the profits over and above $2000 (the logic being that $2000 is the floor since this was made the previous year)?
3. In regards to splitting up the profits, how would I determine who gets what? Would 50/50 split be the only fair approach? Would there ever be trust that we both put-in the same hours? I'm not even sure that this is possible.

Any feedback would be appreciated, thanks.

The first question I would ask is, What is the marketing person bringing to the party...does he have concrete plan of actions that are understandable and actionable?

I would ask you to drill into what exactly you are getting and how it will help increase market penetration.

Should considering a partnership even be an option at this point? I
believe it is way too early to even think about since I barely know
this person, but even if trust was built how would they ever make up
for my 5 years of sweat-equity? I don't know how to quantify that.

If that is a case why not sell him a percentage of the company? You obviously know what you have in it. Appraise your time by fair market value you have put into coding, cost of hosting, management, and profit. If he is really interested make him an offer to sell him no more than 20%. I say 20% because:

1. Your company is still new and if someone offers to buy in for a share down the road you still have 29% left to sell. Never sell more than 51% of your company.
2. You never want to give someone 50% of something that you personally have more time, heart, and sole into a company.

If I choose to simply pay this guy a percentage of the profits for his
promotional/marketing work, what is a fair number? If I theoretically
made $2000 last year, would I only pay him a percentage of the profits
over and above $2000 (the logic being that $2000 is the floor since
this was made the previous year)?

Personally, I wouldn't go in with the guy. Why? I've never scene, from a small business aspect, a marketing individual offer what I can't already do or isn't readily available to someone somewhere. Although I have mostly spent my working life in the print & advertising area, I know how to market and you have a live website up why not try Google ads or something like Buysellads where you can buy ad space to marketable areas that would help with your traffic? In reality what is this guy planning to offer you?

In regards to splitting up the profits, how would I determine who gets
what? Would 50/50 split be the only fair approach? Would there ever be
trust that we both put-in the same hours? I'm not even sure that this
is possible.

If you are really interested offer him a percentage AFTER labor costs monthly for a few months. If this guy thinks and truly believes you have a marketable product he will stick with you. If he lasts a few months offer to sell him a percentage.

From another point of view and experience, if you plan to go into business with this guy, and before you go any further with discussions require a non compete. What's to say that if you start in a partnership with this guy and in a month he takes your ideas, work, and everything you poured into it and starts something just like what you have?

Good Luck!