It is clearly spelled in the FAQ (last time I read them a couple of months ago) that the site will turn into charging to the escorts in some moment. It is a common business model in start ups, you start offering a service for free, in the process adjusting your site to your market needs, and once you grew enough you start monetizing.
So dear friends from Rentboy.pro, let's be completely honest and share that the volunteer and vocational work is just the beginning, the site will become a commercial enterprise.
I am actually planning to do something similar with my blog. I started it just like a hobby to have fun, then found out there is an unexpected interest and potential market. So I just changed my original plans recently. I am planning to keep growing a few months more as an open blog to then add more services and charge a fee. The plan is that in some moment in the second half of this year you will have to pay a very moderate monthly fee to full access to reviews and media (pictures, interviews, and amateur home made porn).