It sounds like you're building a marketplace, where you need to attract both buyers AND sellers. This is difficult because on day one you have absolutely nothing to sell and therefore no one to buy. My suspicion is that these other sites you're looking at are seeding their "service providers," to use your term. We had to do something similar when starting a job board. We had no job seekers (product) and no job posters (buyers), so we had to "fake it 'til we made it" by pulling in job postings from external sites to attract job seekers, then the job posters started to come, then more seekers, more jobs, and so on. But you do need to add value and not deceive anyone. If you help them, they'll appreciate your service.

Consider seeding your site with "service providers" or whatever you're selling. Lots of sites got started this way. I believe Quora seeded their site with both questions and answers for a long time.