Well, I have always dressed nicely (not "richly") when I go to buy something. You just get treated better. I don't get dressed up, but I think it makes a statement and helps me feel assertive.
You can talk all you want about how this poor treatment is judgmental, but I don't think it's the "dress" part. I think it's the woman part. My DH and I have a routine we do when buying a car, where we fake argue, he defers to me, and we threaten to leave. But last time, I test drove and bought my car alone. I went to a Volvo dealer and the guy could have cared less and threw me a set of keys and said to drive it. I could have probably stolen the car. Then I went to a dealer that sold Mercedes and BMWs. They had separate salespeople. The Mercedes saleswoman was a beech and I disliked the car, too. The BMW saleswoman was a little nicer, but I liked the car. I was treated OK, even though I was buying the cheapest model + AWD which upped the price a bit. The dealership split up and now it's just BMW. I must say, the service is great and very customer oriented, even though I'm on the "red team," i.e. the people with the normal priced cars, as opposed to the 100K cars. They listen and treat you nicely there. I also had excellent service at Acton Toyota when I had my Forerunner.
The only time I got treated weirdly because of being in bike clothes was when I went into a boutique in my own town, all sweaty from a 95 degree trip into town (4 miles). But, it was the customers in there, who were whispering about me! The salespeople were great.