Mechanic did unauthorized work; what are my rights?

if you decide not to get the job done there, then before you go call the non-emergency police department number (your local police department) and explain the situation. see what options they give you and ask if they could send an officer out there when you are the mechanic shop and take a written statement of what happened. you could bring the mechanic to small claims court if he/she refuses to release the car back to you. you guys had a verbal agreement, anything that changes in that agreement is a breach of contract, so without a new consent or a written work order for the change (additional $400 for the transmission) there is no contract and you should be free to pick up your vehicle. hope this helps. good luck.