If a car dealership pays $2000/mo for approximately the first 6 months and I don't sell any cars - how will this affect me? Will I need to pay this back?

That will depend on how your salary was arragned in the first place. If your on a draw against commissions, then yes you will have to pay it back. There is on "right" answer, it could be you have a salary of $2,000 or commissions whichever is highest.

If you are on draw against commission, yes you have to pay back any and all money given to you that you don't earn enough commssion to pay. If you are on salary plus commission for the fist few months you don't

Most dealerships that I know of use draw against commission