My first websites (back in 1997) was related with services.
Many plumbers, electricians, builders, painters, and different companies didn't had the money to build a website and didn't know that was important (at that time).
So i have made a deal with them: i build the site, i create the virtual brand - since many of them have horrible logos designed in Word -, i create the content, texts, etc.. and if a client request the service we agree a %.
Well, i have to say that many of this "partnerships" are still live until today, and we have made many others. Basically We receive the call from the client/visitor of the website, we made all the necessary questions depending of the service, and when we contact the company/professional everything is already prepared (location, adress, problem that the professional will face, etc...).
And you know what? Many of this guys don't want, and don't have the time to be checking internet, etc... so we make that job, get our % and it's a real win-win situation.