then your best thing to do would to record a conversation with the garage who did the work asking specific questions such as: "HOW were the bolts drilled?", "What tools were used?", "Who carried out the work?" (this was particularly useful for me as when i then asked the specific mechanic he went against everything his manager stated), "Why did it take 16hours?" etc etc, ask them exploratory questions and not direct questions for if you guide the conversation then they would of prepared for eventualities. i learnt that in criminal investigative techniques, better them dig their own hole as apposed to you telling them where to dig so to speak, and also try adding a convincing tone rather than sounding as if your new to this, it may be a bit late as the work is done but at some point they would crumble with continued interrogation, depends on how hard nosed the guy is though.
