It is possible to be professional without a business suit and proper English, and to do it well. It is possible because professionalism is an attitude, not a song and dance. Many people don't understand that, and we end up with very professional-looking people who are not professional at all.
Let me explain what I mean by that, and what the difference is.
Being Professional
This is what has been drilled into our heads since high school or even earlier, as the definition of professionalism: being interview-ready at all times. That means dressing sharply and being very careful in what you say and how you act, so that you convey a style conducive to business. To put it another way, you never walk into an interview in a tank top, shorts, and flip flops and start the conversation off with "Yo, dude!"
Now that I am out of high school and have had several years of experience in the real world, I have seen and experienced real professionalism from colorful people who wore tank tops and flip flops or who used the word dude, and a total lack of professionalism from people who were dressed in their Sunday best and spoke proper English (and vice versa).
Making a business grow is about how you handle yourself and your business, and whether or not it is consistent.
Being Consistent
Your very first customers are your circle, people that know you on a personal level, have spent time with you, and know all of your quirks and deal with you anyway. You can use colorful language and/or have a dark and slightly twisted sense of humor and it doesn't bother them in the least.
You don't want to change that just because you start doing business with strangers. Minding your Ps and Qs and dressing sharply is not what brings people into your circle. Suddenly becoming a sharp-dressed, silk-tongued businessperson could potentially drive away the customers you already have because it isn't consistent with what they know.
The Difference
Song and dance or professionalism? Song and dance is going out of your way to watch everything you do and look your best, simply because you have a business. It is a facade, a mask of professionalism, if it is simply meant to impress. You are one way when you are doing business, another when you are not.
Professionalism is knowing your business, being personable enough to engage people, and caring about them to some degree. Every person, every time.
How you look or the language and mannerisms that you use is a minor part, and won't matter in the least if you are not knowledgeable about your products or services, or you can't relax and enjoy time with your customers or engage them in real conversation.
There are times and places that it is necessary, and being a professional means knowing what those times and places are and acting accordingly, because that is what it means to take care of your customers. Be a professional.