Sensible advice.
As opposed to conversations that go like this:
Customer "hi I'm thinking I would like to upgrade my spring please. I'm not interested in high rates of fire or stupid FPSs"
Tech "nah mate, you need some siegetek dual sector gears and a high torque motor and replace the bearings with uber leet super hard diamond ones made by NASA. Of course you'll have to change the barrel, the hop, the shims, the gearbox case and the outside of the rifle but it'll be AWESOME"
Oh and someone that will actually deliver on their promises, not charge for a spring change and then just lop a couple of coils off the one that the gun came in with.
Realistic fixed price servicing. We all know it doesn't take 3 days to change simple component so don't try and charge me for three days work to change a spring and wire in a MOSFET.