Someone wants to invest money in my company to startup carpet cleaning business?

I would think that applying divide and conquer principle would benefit you greatly.

Namely. Form a separate company with your partner that will specialize in carpet cleaning. Once done you can look at this forum on the subject of fair division of equity and profit.

So basically what will happen is your clients will hire you to do the cleaning and you will "subcontract" the carpet cleaning work to the company you have with your partner, etc.

The paperwork becomes somewhat of a headache but the profit/equity division should become simpler.

Is this partner currently an employee of your business? It sounds like he is. If so, you may consider it more like a loan. He loans $5K to get the company started in the carpet cleaning business and you pay him (x+y)% of the profits. x would be an accelerated payment schedule on the $5K and y would be ongoing profit sharing. Once the $5K is paid in full, remove x from the equation. Then it is fair to both parties. You get to expand and he gets to share in the profits of the venture, but get it paid off ASAP. If business goes sour between the two of you, it is hard to fire someone you owe money, if you ever need to that is.

You could even put an EOL on the profit sharing if you wish. I know this person would be helping you out, but you could always just go borrow the money if necessary and then you would not be essentially paying interest on this for the rest of your life. That is really what we are talking about here, interest on a debt. Unless you are willing to bring him fully onboard with the whole business.