Do you advertise without a clear strategy? Many advertisers start with facebook advertising looking to hit the big sales numbers. And without a clear strategy you might as well burn your money.
Chosing the wrong marketing objective - You want to get sales from your advertising but if you choose the wrong objective to start with, you end up paying too much per click and never see sales.
Targeting too broad - You can do laser focus targeting in facebook but you need to know how, use the right tools to help you.
No remarketing - You are not retargeting previous visitors with different ads.
Not having a pixel on your website or webshop - When you don´t have a (power)pixel on your website/shop you´re wasting your advertising dollars. By the way you´re not the only one to forget adding a (power)pixel to your site. A power pixel reveals more detailed information about your visitors.
No A/B testing - You should always be testing and measuring. Get informed and use the proper tools.