So this offer is just a way for you to promote your services?
Some people have a service they want to promote. But they don't have money to pay for promotion.
If we see that this service has a great potential, we promote it for free, hoping to get our costs back from % of profits.
In this case we risk our own money, that's why we offer it only for high-demand services
You're doing it for a good cause. Respect you for that. Good luck ; )