I don't doubt you for OR but Federal and WV law makes it a single party consent state. Per 18 USC § 2511(2)(d) and W. Va. Code Ann. § 62-1D-3FWIW - In most jurisdictions - certainly Oregon - it's not legal to record audio without consent. Video is OK though.
If it had not gone so well and a car owner attempted to use this information to claim damages or whatever, the evidence would be thrown out, even small claims.
If this technique is going to be routinely used to keep service tech honest, disable the microphone. Then you're safe.
I would also like to see some precedent regarding recording your own property being against the law.
I don't plan to do this a lot but like I said I was curious.
I don't feel I was breaking any laws but for future reference however I would love to know if I'm wrong.