That's not the case i think. I offer free escrow from the start. One point is that when i would do it solely for earning i would not have done it anyway for so long, it's because i was scammed often enough and i would like to make it harder for scammers. And i know i could manage to prevent alot of scams over time.
The other thing is that i believe that a fixed fee not really means that you will earn more than with no fee at all. If traders are happy they will tip you to show their appreciation. And not a few tip more simply because they like that i don't demand a fixed fee at all. So i would say it doesn't really make a huge difference.