You most probably have decent chance with just being "AirBnB of tour guides" where Tour Guides are hosts and travelers visiting the town are guests. Like AirBnB, host guide showcases his preferred tourist spots in listing and traveler decide whether to book them. The quality is maintained through mutual reviews. You take a cut from traveler's payment and transfer rest to guide. The travelers pays in advance to you, a comfort to guide about no-shows and need to overbook.

Keep it a simple straightforward, easy to understand system. A decent extension to AirBnB lodging business and most probably your exit strategy.