Bryan has installed Sorbo's before. We are talking about a guy that works on an average of ten guns per shift (both rentals and customer guns). So at no point am I doubting his ability to do his job.
If you read my post again, I stated that "our tech won't do anything like modifying without your acknowledgement". And that includes any sort of modified parts (to the piston or hop up in this case). It doesn't matter how "easy" or extensive the modification is. A modification is still a modification and not all customers are comfortable with having their parts (either new or used) modified. We put our word behind our work and warranty our services. A "custom"/Modified job could potentially conflict with us in the future. I don't know how you charge your clients, but we bill by the hour, not by the job. If it requires us more time to do a modification, that time is billed on the customer as well.
ie. a customer forgot that he got us to modify his piston. He ends up selling the gun down the road and the new owner decides to tinker around with it and realizes that the piston is missing a tooth. That person would go back to the seller and complain about this and eventually end up back to us because we are the only ones that has worked on the gun. Some people don't care for an explanation, they just want someone to blame.
I also speak from experience as well, as we have had techs in the past that would do "whatever it takes" to get the guns up and running (ie. customizing parts to fit). And we are still dealing with/hearing the backfire from it today.