I think wearing funky attire is part of the mystique that the public enjoys about having a Tarot reading. It's part of the fun and draws in those who aren't normally customers as well as those who normally come to a reader.
There are those who feel they want to appear more counselor-like and "professional" but in my opinion, that can be more pretentious than dressing in funky attire more along the lines of the Tarot reader stereotype. (Not saying everyone who chooses to dress this way is pretentious, mind you. I said it can be more pretentious.]
On the other hand, if you're the t-shirt and jeans type, go for it if you want to. Nowadays it's an open field how you should look as a reader. Follow your personality. But just don't put yourself out there as being something you're not. If you're not a professional, licensed counselor, then don't give advice as though you are or try to use the cards in such a way that you're delving into areas that are best left to a real professional in the field.
I like looking more of the stereotype. More striking and outside the box, you could say. For parties, especially around Halloween, dressing the part of the Gypsy fortune teller is fun and I think almost expected. Other than that, I like to wear black with striking jewelry and more flashy accessories faintly along Gypsy lines.
I might add, though, that modern-day Gypsies look just like anyone else for the most part, just for the record.
And I haven't done any reading for the public for about a year or more due to other life situations that came along. I never have been a real, full-time professional.