It isn’t a percentage. The dealer takes a car in and does some level of work on it (even if it is just moving it or gassing it up) and adds the cost of that work to the car. They then add a fixed amount to each car for overhead, typically $500-1000, and then add “pack” on top of that, $2000-4000 is what I am used to. So if they take in a $500 car and spend $100 cleaning it, they might advertise it for $3095, with anything above $1100 being profit that is split between the salesman, manager, and dealer.