Does your advert make money?

Your shop or advertising account reports it, often as the conversion rate: orders divided by visits. Use your own figure, because it varies widely between shops and products.

Then a first sale is worth more than its own profit. Add the profit you expect from repeat orders to the profit per sale, but only count what you have seen happen.

There are three levers: pay less per click, turn more visitors into buyers with a better page, or earn more per sale with a higher price or a larger order.