How can I be taken seriously as a woman at the car dealership?

I'm a 27 year old woman but I have a baby face and look about 17. I'm not a car expert, but I want to lease a car soon to be able to travel for jobs. Right now, I don't really know a knowledgeable man to go with me to help out with all the questions & negotiations. I'll try to educate myself on the topic, but what else can I do to be taken seriously and not be cheated??