text: A contract consists of three parts.  An offer, acceptance, and consideration.  The offer was from the mechanic saying he would fix your car for $300.  There was no acceptance, because you said no.  Consideration is something one side gives up in order to fulfill the contract...this would have happened if you paid him for the work he did.  \nThere is no agreement here, no "meeting of the minds"..you do not have to pay, and he needs to give you your car back.  He also violated professional courtesy by taking your car home...\nTry telling him you have talked to a lawyer, maybe that will convince him to give you your car back.