You can most definitely not set up your first campaign, pick the first targeting criteria that comes to mind, and expect good results with a positive ROI within the same day. If you don't keep at, it of course you are going to walk out with the idea that Facebook Ads don't work.
Source: Spent a six figure amount on Facebook over the course of two years.
I have actually literally done this. Just took a stab at an audience, got sales that justified the ad right away.
But we're in a great position with profit margins. They're hand assembled craft items that people generally buy for gifts or weddings, so cost to make is low and sell price is pretty good. Businesses that require high volume on low margins would have a much worse time.
Since the items integrate the buyer's photo, people also often use them as memorials of dead people, but we didn't specifically target that. Yet.
(1) Audience. We created a lookalike audience based on the attributes of our high spenders, which outperformed all previous attempts by a significant margin. I appreciate this option is not going to be available to businesses with no existing customer base.
(2) Tracking. Given the majority of our ads are served on mobile, but convert on desktop or iPad, only Facebook is able to join up the impression and transaction. Previously we had expected to be able to see the attribution in Google Analytics.
My background: I spent a couple years optimizing Google PPC campaigns as a full-time professional when I was at a digital marketing agency. I held Adwords certification for a couple years. I added this so people don't think I just couldn't figure out how to do PPC in general.