You have created a good service. But I do not think any reputed member on this forum will give you 10% charge to exchange his own paypal fund to convert his/her paypal to bitcoin. If you visit other threadsall most all the thread you will see paypal>bitcoin fee is 0.
What abt tx fees? It's not free to send bitcoin. 100$ transaction might cost upto 21 dollars in btc. I believe 10% is low.