Although fashion changes over time and globally there are cultural differences the basic guideline is that appearance should fall within the accepted standards of business attire. The IBM Standard, set in the 50s of “white shirt, red tie, and no facial hair” is still the ideal model for male presentation. For a woman, I am less able to define appearance, but fashion statements should be at the margin of your presentation, not the core. With friends I have joked about the way American female TV presenters wear “Power Suits” but the purpose of your dressing as a salesperson is to build confidence and avoid offence so it is probable that you should be nearer to the Power Suit end of the spectrum than the individualist expression whether the individual statement you are projecting is “sensible girl” or “intellectual girl” or “material girl”.
I am pretty uncomfortable with this topic as it makes me sound like my father, but the ruling principles are simple, you are not dressing for yourself, you are dressing to give “least offence” and “maximum confidence” to a potential customer, who is thinking about doing business with you. One thing I can assure you, is that the businessmen I know hated the short period of time, when the internet was supposed to be a revolution, when they were being told “you just do not get it” by bearded, sandal and jeans wearing techies.
Others who are wondering if these comments are culturally bound I can assure you that I have sold on three continents and more than thirty countries. These rules always apply in presentations or large meetings. The only variations that I make are in small meetings, when I already know the customer, in countries (like for example Singapore) where both climate and culture allows you to jettison the jacket (and sometimes the tie). Even if you have no jacket and tie, do not put your pens in your top pocket, and do not roll up your sleeves. You are presumably not there to fix the refrigeration.