I ran an ad this morning that had a 1.5% CTR. That was great until I investigated the numbers a bit further. I had 35 "clicks", but only 19 of them went to my web site. The rest of the clicks, which Facebook charged me for, all went to FB page. That's not useful at all for my purpose of collecting opt-in email addresses.
So, I changed my approach to CPM. I'm running the exact same ads to the exact same audience. Literally everything is identical except I changed the ad to CPM. Now, my click through rate is suddenly 0% after 600 impressions.