How do I confirm I have the right eyeballs for the price?
Anytime we segment a market for something like books, we're doing a lot of guessing.
For example, a young Wall Street investor may like superheroes just as much as a retired Wyoming rancher or a middle-aged Florida teacher or a firefighter from Kansas. And none of them are gender specific.
I think our target audience needs to be the sweet spot in the matrix - what I call our perfect fan.
I think one strategy might be to isolate that very narrow market segment, and then once you've found them - that is, the ads are working - then begin to add adjacent segments one at a time. Always go slow so you can measure the results. This is also a long game because you have to give the ads time to percolate through the market to see what's working.
Everything in "traditional marketing" says: low-cost over an extended period. Think Enegizer Bunny or Flo.
It's the repetition (frequency) over time. It just works. It has always worked. But it's not so low-cost anymore. CPC can get silly fast. Which is why I recommend the social media approach. It's way less expensive than advertising.
But I'm also on the record for recommending that we do everything we have time for. Ads still work, some are better than others, but they're another tool. And CPC is everywhere, so understanding it is pretty important. The interesting thing is that you may get better ad results by posting on non-traditional channels, so, not Facebook. The internet is a big place.
For example, say your perfect fan is that Wyoming rancher. You might get better results advertising on the same sites as Tractor Supply.
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eta: AI is a great way to research market segments. You can create a prompt to search social media platforms for discussions of your genre and then from these discussions you can research demographic data. Different platforms will have different takes because their own usage demographics are segmented.
And we have to remember, the goal isn't to go viral, it's just to find that core group of fans. The days of Stephen King and Nora Roberts are done and gone because we've lost our monoculture. The goal now is to create our own sub-niches.