08CivicLX

I have a question to ask you guys. well i bought a used hfp muffler from a local guy here in arizona and he claimed it was on his car for only 2 weeks or so. so i decided to buy it for $150 and after i put it on i noticed a few dents in the bottom of the muffler and it makes so rattle noise inside the muffler like something is bouncing around in it. but i only really hear it when its on a cold start up or occasinally at idle. what do u guys think? im thinkin about calling the guy and gettin my money back or is there soemthing i can do to fix it? thanks in advance