Has anyone else seen the new graph for the AMS ad campaigns for KDP Select?
There is also a new column on the table called Average Cost of Sales (ACoS), as a percentage.
The graph displays ACoS, total sales, and total spend.
If you earn a 70% royalty with negligible delivery cost, ideally you'd love to see your ACoS less than 70%. If your ACoS is lower than your actual royalty percentage (after accounting for your delivery cost), your ad is making money short-term.
A lower bid has a chance of making money short-term, though it may not make impressions as quickly.
I have three low-bid ads presently with ACoS's of 20 to 40%. In the past, I had bid much higher, and my ACoS wasn't returning my investment (the ACoS exceeded 100%).
If your ACoS is well over 100%, it probably means you should lower your bid. Unless you have good reason to lose money short term.