Why not try and complain, you cant say they wont do anything if you dont give them a chance, afterall you have the point that you wouldnt know untill you opened them.
Most shops seem to be on your side, when I worked in Halfords whilse at school we allways used to take stuff back, even thinks like ball joint splitters that had obviously been used for a one off job, then returned as "diddnt fit". Also it was surprising (or not) the number of people who came in with genuinley faulty goods, ready for a big argument and hassle who then had to back down when we apologised profusley and gave them a refund or new bit.
Goodluck.