Presentation has everything to do with how you come across to (potential) customers.
If you look sloppy you will be assumed to be sloppy, and this will reflect on your work.
On the other hand if you look like a fashion model then people will assume that you spend time that you should be working on grooming yourself or that you are too expensive.
Somewhere in the middle lies common sense. So, don’t bother springing for the Armani suit, but don’t wear your hiking boots and torn jeans that you used to work on your car either.
The simple rule for an ‘outsider’ is to present yourself a hair better than the people that are employed by the company that you work for. Whatever the dress code of the customers company you adapt to that.
If you think that piercing looks cute, think again. Business tends to be conservative, extravagant body ornamentation is possibly acceptable in an artist or someone with a very well respected reputation, in general you are better off without.
The way to look at it is like this, businesses are looking for stability and knowledge, not for someone that wants to ‘express themselves’, they don’t hire you for your decorative qualities.
If you’re female, don’t overdo it.