BookBub's low-budget ad-testing guide pushes disciplined experiments - small daily spends, one variable at a time, pre-defined kill criteria - so Facebook or Amazon ads become data runs instead of anxiety spirals.
The emphasis is process: iterate creative, watch cost per click and conversion separately, and accept that most tests fail. For authors scared of ads, it's a way to touch the stove without leaving the gas on.
(Shortened and summarised to avoid devaluing the source)