Qualifications
You need to be a people person. You have to be comfortable talking to all kinds of people and to somehow get people to trust you, even though they're walking in the door with a chip on their shoulder expecting to hate you.
Be able to take abuse with a smile and still go for the sale.
Learn a lot about the cars you're selling. Every dealership has an extensive training period where you will have to memorize everything you can about all the cars so that you can talk intelligently about them.
You should be able to read people and know how to push their buttons to get them to decide to plop down a whole lotta money on a piece of metal with an engine.