If I did not give permission for the collision center to fix my car and he still fixed it for more than the car is worth, do I have to pay in full?

He had no right to do what he did. Do you have this in writing on what you wanted him to do? Did he give you an estimate? Did he give you a receipt? Did you give the check directly to him before hand or was he to bill you?  Contact your local attorney general's office and perhaps think about bringing a small claims action against him for breach of contract and fraud if the state's AG's office cannot help you. Look at some of the following damages:

Specific Performance

There are some situations in which money damages are inadequate. Typically, awarding money damages for a breach of contract involving the sale of land does not put the injured party in the same position he or she would have been in if the contract had been fulfilled. Because real estate is unique, one cannot simply go out and buy different property to replace the property for which one originally contracted. In a case such as this, the court may order the breaching party to perform the duties required by the contract. This remedy is called specific performance. Specific performance is ordered by courts only in rare cases in which the subject matter of the contract is unique, making it difficult to put a monetary amount on the damage incurred as a result of the breach. Specific performance is not awarded in personal service contracts. In the previous example, the court would not order the original roofer to complete the job.

Liquidated Damages

In an attempt to set a monetary damage amount in a case in which it may be difficult, the parties may include a provision that specifies the amount of damages in event of a breach. Such predetermined damages are called liquidated damages. For example, a company may put down "earnest money" for space in a mall and agree in the real estate contract to forfeit the earnest money to the mall owners as a damage award in the event of a breach. If the business owner decides not to open the store, the earnest money will be awarded as liquidated damages.

Rescission

In most contract disputes, a court puts the nonbreaching party in the position he or she would have been in if the contract had not been breached. However, there are times when the court may place the party in the position he or she was in before the contract was executed. This remedy is known as rescission. Rescission may be selected in cases in which one party intentionally misrepresents a material fact, for example. If a party has delivered goods or money to another party who fails to perform his or her duties under the contract, the court may decide simply to order that the goods or money be returned. The nonbreaching party then is in a position to contract with someone else.