What is the you break you buy law for michigan?

I was at a consignment shop (used clothing) and while trying on a dress the zipper broke, and NO the dress wasn't too small for me. I informed the manager and she told me that I must pay for it and I refused. There are no "you damage you buy" signs and who's to say that the previous owner or someone that tried the dress on before me didn't loosen the threads near the zipper (the actual zipper didn't break, the threads around it got caught in the zipper) My way of looking at it is this: if you test drive a used car and a belt breaks while your driving, do you have to repair the car or purchase the car? Obviously, the answer is no. I would like to read the law myself, so if someone could answer with a link, that would be great! By the way, Im not saying that I have no responsibility what so ever, I would be willing to pay for the cost to get the zipper replaced or pay the previous owner what her share would have been from the store if they sold it, I just don't think the store should profit the extra $50. Thanks!