While I don’t agree with everything Bijou Drains said, the following explains why I don’t fault him (her?) for being upset.
To me this is a MAJOR failing on their part. Aside from a few long-term-super-good-relationship customers where I know it’s okay, I wouldn’t DREAM of surprising a customer with a bill for something where the price wasn’t clearly understood and agreed to before the work was done. It flabbergasts me that any shop would do this, and I would expect that the customer is not legally obligated to pay for charges he didn’t approve.
I still think it’s questionable that the shop should be liable for the lug stud repair, but in my mind they shot themselves in the foot by proceeding without proper approval. I don’t think the customer can be held liable for the repair charge.