The search engines’ rules around trademark use in paid search ads in the United States are nuanced and complicated. Unless you work with them every day, as we do, it can be difficult to know when an ad complies with the rules.
What is crystal clear though is the frustration you have when you see a competitor showing up on the search engine results page (SERP) using your branded keywords. Infuriating? Yes, but is it allowed? It depends.