Not a tutor myself but Ive engaged home tutors. So far Ive heard a few cases of tutors being "mistreated" by their agencies..some good some bad. Recently, Ive engaged a tutor from School of Tutors and asked my tutor how's the agency and she's all thumbs up. Claiming she's now able to really build up her profile as a tutor given that all reviews from parents who have engaged her will now appear in her own profile page...and she can use their reviews to promote her tutoring service. kindda like building her own business and not rely and wait on agencies' recommendations. So it's win-win for her and the website.
If you are tutor, you should take a look at their website.