Help others win a 5* Star Seller achievement!!
Simply go to a festival spot, open the autoshow/garage/auction menu, open an auction.
You can go down two routes. Buying the car out immediately for a higher price or having an actual bidding war which saves money but wastes time (between one and 24 hours)
Both will work. Just win an auction and collect the car.
Achievement should pop when you place the car in your garage.