I've discovered why Amazon has been spending my entire ad budget day after day on one title yet there are no sales. The search terms for bdsm, erotic, and others of that ilk that include the word "romance" have been matched by Amazon with my keyword "romance" and the same for those that include "western."
This I think is the result of a change in algorithm. The title of my first in series is somewhat provocative in an old school way, but the previous 90 negative target terms I had were enough to prevent the kink audience from clicking and spending my budget. Now I've had to go back and add several dozen new "negative phrase" and "negative exact" terms to the list. Plus bdsm, which is a huge stretch for the algorithm when all my descriptive keywords are sweet, clean, mild, etc.
Meanwhile, a Fussy Librarian ad for that same title during a Kindle Countdown has resulted in extremely pitiful sales--a mere four so far. The Fussy ads don't cost much but for my books they also don't do much.