Love 'em or hate 'em, any bookseller who doesn't deal in romances is making a mistake. Romance readers are steady, voracious consumers.
Unfortunately, to sell these books you have to --bleah-- spend time at least skimming them, because readers are very picky about content.
These days there are websites for it, but back in my librarian days we attended seminars about why people read the fiction they read. In normal libraries (ours was not terribly normal) there was a high demand for what the profession calls "readers' advisory" in which, to give an example, somebody who loved Outlander comes in asking for more books like that. You, the Advisor, need to be able to zero in on what the reader means by "books like that": Was it the time travel plot device? the time period, the Scotland setting? Something more difficult to articulate?
Our library almost never got such questions, but the seminars were too much fun to miss. The guy who ran them was a true comedian. He used The Hunt for Red October as an example, and started by summarizing the plot: the Soviets want to conceal the fact that the commander of their high tech sub is trying to defect to the US. Jack Ryan, a mid-level CIA analyst, figures out that this is a defection, but Ryan has to fight his way through the thick-headed upper management and the Joint Chiefs of Staff trying to get somebody to listen, and then has to manage a touchy political situation while playing the cards just right, to keep the Soviets from destroying the prize before the US can gets its hands on it.
Here you have to picture our seminar leader assuming a posture and a voice like Jack Benny:
"Now," he said, feigning puzzlement, "why do you suppose that white, middle management males went crazy for this book?"
It was the delivery. You had to be there. The room cracked up.
The seminars naturally focused on the kind of reader response to fiction that librarians could actually help them satisfy. We're talking what's called "genre" fiction. Romance, mysteries, technothrillers, fantasy, sci fi, etc.
Most fiction genres (I'm not so sure about romance, but that may be my prejudice) can produce something innovative and mind-expanding. "Formulaic" is only a subset of "genre fiction." And some very intelligent readers use genre fiction to take much-needed mental R&R, so we learned long ago that we couldn't make assumptions about the readers. We did find that when people seek a semi-meditative, emotional auto-pilot type of reading experience, they're more inclined to ask for book suggestions than when they're looking for a mind-challenge.
Advising them meant getting enough information out of them to identify the attraction a book held, and that's not so easy when the attraction is on a more emotional and less cognitive level. Romance readers are very specific as to the plot and character components they like. Sometimes the time period or setting will get the customer a big enough stack of books to send her home happy, but often it's a more subtle factor. She might like poor-plucky-orphan-girl stories no matter the setting, or arranged-marriage-turns-into-true-love plots.
So a book is set in the American West? Not enough info! You need to identify the sub-genres. Does the woman tame the most powerful authority figure in town? Or is it an outlaw bad-boy she overwhelms with her charms? Hey, a reader who craves outlaws isn't going to be terribly interested in our schoolmarm thawing out the cold local sheriff.
Time travel romance is the hot "new" thing in a series of historical romance sub-genres that feed the urge to escape the bonds of "civilized" society : a way out of one's Dilbertian cubicle is supernatural transport to a wilder, more primitive era.
If the whole idea behind this level of pleasure-reading is to bypass conscious thought and go directly to Primal Urge Central, that explains why romances tend toward types in their elements and, whether they're sexually explicit or not, toward those things innocuously called traditional values.
For a seller, this means skimming some of the worst stuff on earth. An inconvenient husband is always an SOB but, even to someone we'd call an abuser in real modern life, marriage is sacred in these novels. So he must change radically into a tender appreciative mate, or die or, in one case, turn out to be gay. That book's POV made gay orientation a synonym for villainy. If you want sympathy for a character forced into a societal role that he can't fill, you won't get it in a bodice-ripper.
Categorizing romances: it's not a pretty job, but somebody has to do it!