
Quoting
Mr. Knowitall
It sounds like they understandably wanted to help the OP avoid a financial loss, but at the end of their review they determined that they were unable to offer any such assistance and had to return the motorcycle to its owner in 'repaired' condition.
You claim that you spoke with a lawyer, and that your lawyer advised you that you had a good chance of prevailing. You should pose follow-up questions to your lawyer: "What legal theory should we present in court, that will allow us to prevail" and, if the answer is "Unjust enrichment", "How can we prove unjust enrichment when the owner of the motorcycle did not know either that we had his motorcycle or that we were performing repairs upon it?" If your lawyer proposes another theory, tell us what it is and we can help you determine the elements of that theory such that you will know what you need to prove in court.
We get that you want money for the parts you installed. We understand why you want money for the parts you installed. Not all of us are unsympathetic to your position. But the gulf you must nonetheless cross is how you can prove that you are legally entitled to any compensation for the parts you installed. As you have been told, and shown through case law from your state, merely having repaired somebody else's motorcycle is not of itself enough to legally entitle you to compensation.