Ying took her logging machine in for repairs. A week later she got a call from the shop to tell her that the machine was fixed and the bill was $4500. Ying had left strict instructions with the shop that she must approve all work before it was done. What rules of contract determine whether Ying is obligated to pay the bill? If she refuses, what are the shop’s remedies? What safeguards and risks are involved in those remedies for Ying?