The most important part of paid advertising starts with understanding a few key pieces of your company's finances. First, you need to know what your average profit per sale is. Next, you need to know your conversion rate -- which is the percent of people that inquire about your product and then actually purchase it. Finally, you can then assign a target cost-per-acquisition that allows you to maintain a profit. Your cost-per-acquisition is equal to what you’re willing to pay for each closed deal. Then, instead of worrying about paying $15 per click, you focus on keeping your cost per acquisition within your margins.