I don't know whether it's just me and my frugal ways, but I can't seem to get over the fear of wasting money on ads.
Partly it's because there's no tangible benefit. If I spend on a cover, or an audiobook, or editing, I get something in return. On the other hand, when I put money into advertising there's this nebulous idea that it SHOULD benefit book sales, but the hard data never backs it up. Any extra income will be spread over several days, weeks or months, and I can't point to a bunch of sales and say 'THEY were thanks to the ad'.
It's even trickier now I'm in KU, because page reads aren't shown on the AMS dash.
As an example, I'm running one auto-targeted AMS ad which ran up US$25 in costs yesterday. (I saw the amount rising and for once I decided ... stuff it, let's see what happens.) That generated 43 clicks.
The ad is for a first in a series of ten novels, so it could take a month or more for some of the people who clicked the ad to read their way through the entire series.
And here's the thing: if just 2 of the 43 people who clicked my ad DO read the entire series, that's a $15 profit.
Every business bone in my body is screaming at me to spend that much and more on ads every single day, but my brain just won't let me. I see the amount I owe AMS rising and put the brakes on.
Just to be clear, I've never spent more in ads than my incoming royalties. I'm not talking about putting myself into debt, just an unwillingness to put larger sums into advertising, even though it probably would pay off.