Since algorithm updates started in 2015, the most important factors in a PPC campaign have changed. Be sure to ask your candidates what are the most important statistics they look for in a good campaign. If Quality score and Relevance are not the first or second answers, then your PPC candidate still adheres to an old-school of thought where "as long as I am paying for top ranked keywords, we will be fine."

Truth of the matter is, Google cares more about now how relevant your link is to users searching those terms. If many users click 'back' immediately after clicking your link, your page is not helping them solve the problem they are searching for. High-quality ads cost less and rank higher on the search engine results than someone even willing to pay more.

Check out this answer from Google to learn more.
https://support.google.com/adwords/answer/6167123