What is the ruling on a sales representative who sells a product he does not own, receives its price, then buys it and delivers it to the buyer, taking a profit from it?

The salesperson is an agent of the company owner. If he sells a product that is available with the company, there is no harm in that, and the profit goes to the company. However, if the product is not available, it is not permissible to sell it, based on the hadith: "Do not sell what you do not possess."