“A lot of times cheaper CPMs mean worse traffic — not always, but a lot of times. If there's a big decline in performance, I check if there was also a decline in CPM. Google's algorithm can blend high-quality and low-quality inventory and average it out. People are like 'I don't want the crap' — but you have to actively manage it.”

Cheaper CPMs in UAC are a warning sign — low cost usually means low-quality display traffic

UAC blends Play Store, Search, YouTube, Admob, and Display Network traffic into a single averaged performance number. If CPMs suddenly drop, the algorithm has shifted spend toward cheaper Display Network inventory. Black monitors CPMs as a leading indicator of traffic quality — a counterintuitive practice since most UA managers optimize for CPI. She also audits specific sites serving ads and excludes spammy placements.