...with AMS I just can't seem to spend any money (a common complaint.) I think it's because I write in a couple of niches, and it's hard to find similar authors to target - especially on Bookbub.
Plus, while my target authors might be doing well, there aren't hundreds of people a day viewing their product pages. I can't scale up.
These are my issues with AMS. I have two completed series. One is pretty niche (adult political dystopian thriller) and has few keywords (about 200) because I just can't find many similar books or authors to target. Most dystopian that does well seems to be YA or coming-of-age related, but I can't target those readers since my books are so different. This series sells, but not too well. If people read it, they tend to like it. But not many people pick it up to begin with. I've long since given up on it taking off, but I still set AMS to a budget of $250 per day.
My epic fantasy series does
much better and is the reason I can pay my bills. I have tons of keywords, many more authors/series/books targeted, and a budget of $1000 per day. It sells well, but the authors I can afford to target have smaller readerships. Targeting the authors with larger readerships is too expensive. I'm willing to spend a lot of money on advertising as long as I make a profit, but I max my ads at $0.60 CPC. I can't justify paying more than that for one person just to "consider" a purchase. Some keywords
never get clicks despite the fact they are highly relevant. Others I'm not sure about get clicks and sales. None of my campaigns ever max out their budgets.
I can't seem to scale up, like you said. The good thing is that I don't feel I need to right away. The most consistent and best method of marketing I've seen is releasing something new, so that's what I'm going with for now. I just released a standalone book that has ties to the fantasy series, and had some of my best sales days ever over the past two weeks. Fans of the series are buying it, and new readers are buying the standalone and moving on to the series. For some reason, my new book is doing fantastic in .de, so I'm getting lots of follow-up sales there of the series. I'm currently 24K words into the first book of a trilogy that will also tie in to the others, and I'm trying to stick to a schedule of four releases per year. Between always having a new release in that 90-day cycle and consistent marketing, I'm hoping to scale up over time.