If you don't sell more than 40 units per month you don't need the professional selling plan. You will be charged $ -.99 per unit sold. It doesn't matter if you are a sole proprietor or a company, you can sell without problems. If you reach more than 40 units per month you upgrade your account to professional and you will be charged the monthly fee. I suggest you go to "Learn" in your seller central and watch the videos in seller university. There is a lot to learn and there are many traps selling on Amazon.