Facebook Ads can be very effective in generating sales. You can retarget people who have visited your site but have not purchased with compelling offers. Additionally, you can create a Facebook Ads marketing funnel that is proven to drive sales.
Data on the success of Facebook ads is not easy to find or very readily available. There is general agreement that you will likely be able to generate more sales if you can create an ad that will go “viral”. These viral ads get shared over and over which is all basically just free advertising for you. But, you have to be very clever to be able to do this.
What Facebook ads are more successful at, is generating leads or driving traffic to a website and to get people to opt-in to your email lists. It is hoped the increased traffic and email recipients will help generate more sales and most of the times it actually does.