First:
Shit, shower, and shave. Dress in business attire. Don't wear your watch. The one you're wearing is not appropriate for this type of dealership and a dead giveaway.
Second:
Walk or rent a decent car to drive to the dealership. The car you're driving is not appropriate for this type of dealership and a dead giveaway.
Third:
Have a friend call your cellphone once every five minutes, and once every three minutes. Talk like you are dealing with stocks, throw out figures, laugh with a sense of concern, etc.
Fourth:
Don't seem anxious to drive a specific car. Browse and lead the salesperson on.
Fifth:
Gentleman, start your engines.
