The feature I'm going to talk about in this post is not new (was released a couple of months back). However, on daily conversations with E-Commerce Owners and marketers, I noticed the vast majority of them still don't know about this easy and free trick.
Since all the Cambridge Analytica scandal was uncovered, which had its decisive or critical point on March 2018, Facebook is working on being more transparent. That's one of the main reasons why the Info and Ads section was added on Facebook Fan pages. The era of "dark posts" is close.
Going straight to the point, if you want to spy on your competitor's facebook ads, go to their fan page and on the right side column, look at the Info and Ads tab. (normally the last one)
By clicking here you will see the latest Ads of your competitor. The only thing you will not see (yet) is the social interactions on their Ads (likes, shares, comments...)