I'd say go and feign interest in some used cars; watch what they say, watch the process... just watch and understand as much as you can, WITHOUT buying anything!
Read up on some books on persuasion/high pressure sales, look up the general financial techniques they use (ie I'm under the impression they give you more cash for the car you trade in than it's worth, but recoup that by overcharging you on the car you take home.. and then there's the $20k balloon payment at the end... etc).
Go into some lots, ask if they need a hand doing something else - paperwork or cleaning or something, see if you can get to know the procedure.
Information, information, information.