Crappy thing to go through. I would speak to the owner again, heavily bluff your importance/connections in the automotive universe and calmly advise that if he doesn’t make this right, you will do everything in your power to reflect this experience on his reputation (Yelp, BBB, other online review sites, posts on automotive forums, etc). That’s your best leverage in this day & age.
If he doesn’t make any attempt to address your loss in a meaningful way, follow through with your threat to the best of your ability.
As far as legal avenues, taking him to court, surveillance footage, etc, I wouldn’t even bother. I get everyone here wanting to vicariously feel your shining defeat over an outrageous injustice, but who has the time or brain cells for all that? Moreover, you don’t reside in the area...and you’d probably lose anyways as it will quickly become a “he said, she said” deal.
Better to just slam the s**t out of him and move on with life.
Good luck with the black coil and sorry this happened.