I used to wear a suit & tie when I visited a new client. After they got to know me I would switch to casual (but not T-shirts or shorts). Around 17 years ago (not sure exactly - my online billing system only goes back to 1994), I went to a new client on one of the hottest days of the summer in a suit & tie. They were quite a bit more casual. After that I said "forget it" and I never wore a suit & tie to a customer (old or new) again except when specifically asked to do so (e.g. customer has a big meeting with another company and everyone dresses up for the occasion). Most of my business is word-of-mouth, so I figure even the law firms have some idea of what they're getting before I show up the first time.

That "last suit" customer is still with me - 2 owners and 4 moves later. If I showed up now in a suit & tie they'd probably wonder what was wrong.