Reporting tax evasion to IRS.?

Ok here is the deal. A mechanic is working on my motorcycle on the side. He is now trying to hold my bike hostage because I refuse to pay for work that I didn't approve and I have evidence that I didn't approve it. Long story short I want this guy to pay for the problems he is causing me. He hasn't given me any reciepts for the work I paid for so far nor has he charged me taxes or anything else. I'm sure he doesn't plan to let the IRS know he made that money. I paid him over 500 dollars so far with another 300 that's supposed to be due. Is there anything I can do?