Can’t say you’ve been ripped off.
How can anyone else say how the car has been driven. I can destroy a perfectly good clutch in 50 miles on any car (and I have done, but we won’t go into that)
There may be other reasons for the clutch to go, oil from the engine or gearbox fouling the plates, or damage to the flywheel a present from the old clutch. It could be the clutch it’s self, but to diagnose it you’re still going to have to pay to get it taken apart, then once apart establish what’s caused it.
No matter what has caused it, in all cases it’s going to have almost zero to do with the garage that fitted it. As you say it’s been working fine for 2years and 13,000 miles.