On liens, yes, the mechanic may technically be able to put a lien on a
vehicle,  but how easy is it to enforce? And consequently, how many
mechanics pursue that avenue? Whereas with real estate, a mechanic's lien
has real power. There's absolutely no way you can sell the building without
paying it off. And you can't just take it for a test drive and never come
back. Other than lenders, I haven't heard of any cases where there's a lien
put on a vehicle, though there must be some.