What is a mechanic's lien?

Question

How can it be done, who usually does it and under what circumstance is it done?

Answer 1

http://en.wikipedia.org/wiki/Mechanics_lien
A mechanics' lien is a security interest in the title to property for the benefit of those who have supplied labor or materials that improve the property. The lien exists for both real property and personal property.

Basically, a mechanic can put a lien on your automobile, if repair and parts made by the mechanic hasn't been paid for.

Each state has their own laws concerning these types of liens:
http://www.asashop.org/legis/lien.htm

Answer 2

Generally... you take your car in for service and the mechanic fixes it. You can't get your car back until you pay for the service, the mechanic holds a lien on the car to compel you to pay the bill. The specifics of a mechanics lien will be detailed on the repair order -- in the small print. It's there. If not, the mechanic can't hold the car and has to take legal action to get paid.