text: when selling a car in ca when is it neccessary to sign a "power of attorney" form? i am trying to sell my car and the buyer wants me to sign a 'power of attorney' form. i have sold several vehicles before and have never had to sign one. what would this signature allow them to do and is it neccessary that i sign it? thanks!! your signature would authorize them to do some act in your name. it's an invitation to a scam. don't do it.