How to determine if high ad frequency is causing creative fatigue

Two weeks after taking over paid social media ad campaigns, I encountered an easily underestimated problem: CTR was dropping, CPM was rising, sales said lead quality was poor, and the media buyer's first reaction was to increase the budget and change the audience. It wasn't the kind of failure where the cause is obvious at a glance; it was more like several small oversights stacked together. I…