That's not entirely true bro. My friends family, her, her husband, 3 year old girl, father and mother went to the showroom the other day in t-shirts, shorts, bermudas, china ah-pek slippers, and they layan very well. I think they are trained not to assume because no one is going to be dressed to the bone just to buy a car.surely need to wear proper attire.. if not, sure the sales person will look u upside down... unless you're the real thing and come from deep pocket united... then wear a sarong and face like Japanese slippers won't give u any problem...
In the end friends father ordered a Panamera S with his China ah-pek slippers, t-shirt and all.
Never assume if you're a salesman! You'll never know who you'll come across