Sure. In GTA 5 story, selling cars can be done at particular locations, mainly the Los Santos Customs. You drive up to the place, and if the car is eligible for sale, you'll see the option. But there are limitations. For example, stolen cars that are marked as such might not be sellable. Also, the game has a system where the value of the car is determined by various factors like its make, model, and how much it has been customized or damaged. So, it's not always a simple process of just driving any car to the shop and getting money for it.
Yes, you can sell cars in GTA 5 story mode. There are certain locations where you can do this, like some of the Los Santos Customs shops around the map. Just drive the car you want to sell to the shop, and there should be an option to sell it, but keep in mind that not all cars can be sold, and the price you get depends on the condition and type of the car.