I do computer freelance, but these days I don't get a lot of customers. Since I know how to fix iphones, I would say it is a beneficial and risky business. Beneficial because it is a good source of income and risky because it is dangerous if you brick someone phone and not being able to replace it.
I charge $60 for iphone 4 and 4s screen, $100 for iphone 5s and 5, $120 for iphone 6 and $150 for iphone 6s.
I also tell my customers whether the parts are OEM or premium replacement. I also ask them if they have Apple care before I proceed.
They accept the repairs on their own risk and I also offer a 30 day guarantee warranty.
Hope it helps you.