Years ago, I hear an adage that's stuck with me: you only have one chance to make a first impression.
When you think of it, if you'd gone to that call in a sports jacket and turtle neck only to find the entire customer contingent in 3 piece suits ...
What works is "middle of the road". Don't be under-dressed and don't over-dress. Whatever is current in terms of hair styles, etc.
In fact, when I was at Apple Computer, we'd frequently be asked what the dress-code was by customers coming to a presentation! It isn't inappropriate, if you're not sure, to ask a prospect about the dress-code.
I would never grow a beard while on-the-job but I wouldn't frown on someone with a full beard (assuming it's a male) ... lol!
Good luck & good selling!
Pat