Initial thoughts are that there aren't really any problems, diesels are known to stop with a shudder (probably down to heavier parts and the higher compression ratio). If the garage can't come up with anything, then it's likely nothing. Do you think a garage would pass on a profit just because they can?
How do you know that this shudder, which again, is completely normal for a diesel, is the source of parts damage? Have you ever experienced a HGV engine shutting off? It's certainly more violent than this. How do you know that the parts were fitted properly and that poor-fitting wasn't the cause of premature wear?
Hell, given that a shudder is normal for a diesel, how do you know that you didn't notice the shudder until after it had been to the garage?
I certainly hope you weren't jacking the car up by the exhaust either...
My advice? Get it checked by another trusted garage if it concerns you that much. If they find no issue in regards to the shudder, it's normal and you never noticed it until after it had gone to the garage, thus the premature wear is likely down to poor fitting, undiscovered worn parts causing other parts to wear prematurely or faulty parts.