When I go to clients to fix their stuff I try to remember to have clothes on. When I have to meet with clients to discuss contracts/bills etc. I have to dress "business", which for me is something reasonably clean. When I have to meet with money people (banks etc) I have to dig the suit out of mothballs. At home (work a lot there) or in the shop I wear whatever I have on - never think about it.
I once went to a new client right after a bank meeting, wearing a suit, and they were really suspicious - they didn't think I was "techie" enough to work for them. Kicked off my shoes, left the jacket on the boss's desk, used my tie to rig the cage door open, and wrote a few phone numbers on my shirt, a little more my speed. They're still a client. Law firm.