Let's say that a foreigner wants to sell products or services in US using a company there to save his/her clients of importing his products/services. Yet this hypothetical entrepreneur does not stay in US all the time, only when he goes to sell his products/services under a business visa. Which are the rules of such operation?
You cannot work for a US Company on a B1 visa, that would require a work permit (H1B). Of course you can set-up a US company, but I don't see the advantage in your scenario, it would only make sense if the company would have employees in the US. As a rule of thump a B1 visa only allows you to do to non-manual labor, like attending meetings, soliciting sales, negotiating contracts etc. You cannot run a business or get paid by your US business.
What kind of products are you selling? It should be relatively easy to just ship them from overseas using a courier service.
Could you please clarify the way you want to use the US company? If the company has no employees, how is it supposed to do business? Somebody has to sign contracts on behalf of the US company or do the paperwork to import your products and you can't do either on a B1 visa.