Example : Market price 15k for the car, You purchase for 12k and sell it for 12k after 6 months( depreciation)
I'm assuming your end goal is to make money, right? If so, then your 'plan' doesn't make any sense at all. You're buying a car for 12k and selling it for 12k? In the 6 months you have the car, how much would you have spent for insurance, gas, and maintenance? You'll probably end up loosing money.
How will you make money?
Yes it's possible, but your business model generates no profit.
Why would buying it and selling it for the same price make any sense?
that's where dealers find their cars to sell
That doesn't make sense. You didn't make any money doing that.