I second that.
I once had a service on my Honda. My front pads were VERY low, but I was driving to JAE the next day to take delivery of new uprated discs and pads.
Brakes were going CRAZY on the drive there, I knew there was something wrong.
Got to JAE, took off my wheels to stick the new discs on. They had put the pads back on THE WRONG WAY ROUND.
i.e. metal to disc rather than pad to disc!!!
Luckily we filmed it/took photos of it all as we were doing a "how too" thing for the delsol forum.
Anyway, went back nice and calm, with the discs and pads, spoke to the manager, told him I had just spent £200 with them on a major service and another £200 on discs and pads.
They gave me the service money back, the money for the uprated discs and pads back (which I was buying anyway) AND credit note for another service.
In exchange for the wrecked discs and pads.
I went in there, asked to speak to the manager in his office. Kept it quiet yet firm. Let HIM decide what to offer me.
Very sorry to hear about this, but as Dan says easy human error. Go and see what they say