Ask the car dealer to remove the badge
The best thing would be to ask the car dealer to get the metal badge removed before you buy the car. However, most of the dealers would not agree to this. You can ask them once or twice but chances are that they would not remove the badge which markets their own name.
Use hair dryer on the metal badge
First of all, you need to plug in a hair dryer and direct the heat from it to the metal dealer badge on the car. It is important that you direct the heat at the badge in a horizontal motion and not in one place at a longer time as that could damage the surface of the vehicle. The direct heat will melt the adhesive with which the badge has been glued to the vehicle and will make it easy for you to remove it.
Remove the badge with a plastic knife
Carefully slide a knife behind the metal badge and try to push it in the outward direction. Make sure you use a putty knife for this purpose as a pointed knife could damage the paint on that particular spot.
Remove lumps of adhesive with hand
When the metal badge is removed, try to remove the large lumps of glue with your hand. Do not try to pull it if they do not come out easily as that would scratch that area. Use the hair dryer technique on these areas again.
Apply car wax on the spot
Use car wax on the affected area and polish the area nicely to give it a shiny look.