3rd Jays comment if they told you via phone what diff to get and it's not recorded I would say they will win. and you will have to pay up. But if you have it anywhere written down by them that it was that Diff they told you to get, or even on a receipt issued by them for fitting it i believe that would stand as evidence that it was in fact them that told you to get the wrong part. If you don't I think you will have a 20% chance of winning myself, I think they will play the you got the wrong part and it's not the one they told you to get :(