I dont see how you can sue for something like that. Yes they sent you the wrong product, but it was his own fault for putting them on and not realizing that they were the wrong thing. He said that he noticed they were about 1mm thicker but he used them none-the-less. Therefore, since he used them, semi-knowing, that they were the wrong thing, it would not be their fault.
In a sense, that is like you buying a cable for your HD and they send you a floppy cable, if you installed the floppy (somehow...) and it broke your HD, you couldnt sue the company that sent you the wrong cable. I would have to assume that if someone bout the SLK-800 and saw that the pads were messed up and asked for new ones, they should atleast know what they should look like. You could always compare what you got from what you had, and if they differed, then you ask them why they are different then they would tell you, "oh, we sent you the wrong pads, we will ship the correct ones out today" and you would have saved yourself some money...