When the customer leaves, what would you rather have, "he was well dressed but clueless - I'll never come back" or "he had a unique style, but he knew what he was talking about, I'm definitely going to come back here again".
The greater risk for the business is that the customer will walk out before he's even begun to ask a question. Or you will solve the problem, but the customer feels uncomfortable around you and chooses to go elsewhere next time. (I've been guilty of this. To identify my error required a third party who knew both me and the customer.) Given a more complex problem, without the right combination of dress, tone, and language you might not get the customer to open up sufficiently - imagine a doctor dressed as a gothic vampire asking to listen to your heart

. The uncompromising man may be required when revolution is in order, but the average business would do better accommodating for its clients, not battling social norms.
The point about being able to be talented
and well-dressed has already been discussed. When my brother was about 6 years old, I remember his visiting a friend's house and being asked by the quite proper mother, "Would you like ice cream or cake?" Confidently he answered, "Both!" The response was shock. As we grow we fill our minds with false dichotomies, to the extent that it's almost considered
rude to expect that someone perceives a wider set of possibilities.
I don't mind if someone doesn't know something, its when they try to fudge things, that when I get peeved of.
Indeed, a divined substitute for a competent answer is the worst possible response. As CalBoy's example illustrated, I was simply arguing against assessment on the basis of precise knowledge of imprecise details; I should probably have quoted more than just your post

.
As for those who work with me day-to-day, I couldn't give two hoots about how they dress around me, but I'm talking from the PoV that people don't just have to interact with me (a blessing for them, I'm sure

). Even then, people's choice of public dress is
a priori based on how they wish to be perceived, which in turn reflects their character, so I'll usually find vague correlations between choices of dress and attitudes.