Day of the Week
Have you studied user behaviour for different days of the week? I guarantee you that most of the time there will be a correlation and a skew towards cer tain days performing better than others.
As an example, we have found for products selling physical items that need to be shipped, Thursdays – Saturdays were the worst performing days with CPA almost triple compared to a Sunday -Wednesday. Why? Well.. people didn’t like to wait 4 days to receive the item because generally no one delivers or ships on the weekend. Makes sense right? There is a good chance a lot of advertisers may not understand user behavior and be spending top dollar on days where a decent CPA was achievable. This will vary from Display to Search, with display’s impulsive users less likely to care when they get their product… as long as they get it.
What you can do to fix it:
Understand your day of the week reports and get yourself thinking ‘why’ the behaviour varies as it does. Understanding and asking yourself these questions is a great step towards improving your campaign.