OP, I get that you are trying something new here with your service, but a 10% commission sounds steep. Maybe you could try it out at 5% first though. Like a promotional period. See if you still get takers and cover your costs. If it works without issues and once you establish a reputation, the fee could gradually increase if needed. People will probably stay and accept higher fees down the line.
I would agree here that a 10% fee is quite expensive. I'm pretty sure there are other, but also cheaper, options. At the same time, I think that the moment a good reputation is established, there is no need to increase the service fee, because the larger number of users and transactions will compensate for the necessary profit for the business.
Otherwise, what is the position on KYC here?
Is there a risk of blocking transactions if you think that the coins are not "clean" enough?