In many jurisdictions there's a major problem with taxation: if you sell something from a person to another, you can usually do it tax free, at least on a small scale. If you create a company to facilitate this process, and the company acts as a middle man by buying the things from one person and selling them to another, the company probably needs to pay value added tax from the sale. In Finland, for example, that's a 23% added cost. And if you take commission, you'll need to pay the tax for that as well.