I had a pre-buy inspection done on my plane. The shop missed some items that turned out to be very expensive to repair. The exhaust shroud was in very bad condition and totally needs replacing, and the alternator belt is badly cracked, almost all the way through. These were very visible from the outside and did not require disassembly to see. I called the shop and their response was, "oh well. Sorry." Who can I file complaints with? I filed a complaint with the FAA Hotline Reporting. Where else can I file complaints to get them investigated?