I had a 36,000K service on Friday last week and found that they had replaced the front left pads and the rear pads, but left the front right with a note they needed chaning next service.
This provided an interesting braking effect thanks to the combined brakes. The brakes fist act on the right side, [which thanks to the old pads was fairly mild] then the linked barkes operate the left side [which is rather more agressive thanks to the new pads].
Trust me, it's unusually, and not recommeneded.
Anyway it turns out they hadn't done the clutch/brake/coolant fluids [specifically requested, and part of the standard service] so I took it back [they agreed to do those for free!]. I explained that I wanted the right front pad changed as well, and why.
late yesterday they called to say they didn't have a right front pad and asked if they could keep it overnight. I'm now sure the reason the right front wasn't changes was they didn't have one!
Now it's turned really expensive as I need a new regulator! There goes all my surplus case into the XX again.