Hard to swallow pill time, guys! Buckle up!
I have now stopped reading two books that are nothing like what I wanted to read. How did this happen? Well, you see, like any other reader on the face of the planet, I search for what I want to read by genre and category. If I want to read fantasy, I search for fantasy. But then, I read the descriptions of both of these books in the fantasy section, descriptions that sounded like, "Whatsherface is the blah blah of the whatever kingdom and is facing a wild challenge. Encountering evil, magic, and extraordinary beasts, Whatsherface must find a way to save her home from the bad thing." And I'm like, "Heck yeah," and I buy it.
Only to open it up and read fifteen to (dear God) forty-eight consecutive chapters about the not-so-well-paced blossoming relationship between Whatsherface and Dude Who Wasn't Even Vaguely Alluded To In The Description—with a background of magic and danger with minimal detail. So, guess what I do? I close the book and I leave a not-very-nice review, like every reader should do in this situation.
Here's the thing: there is nothing in the world wrong with writing a romance. Millions and millions of readers are genuinely ravenous for romance books and seek them out. I am not one of those readers. When I pick up a book in the fantasy section with a fantasy description, I expect to read a plot that is geared toward fantasy and what was said in the description with subplots of romance between characters. In fact, I actually love romance as a subplot and enjoy it immensely. Very rarely as the main plot. So, if what you've written is actually a romance, please, for the love of all that is holy, market it as a romance, put it in the romance section as its main genre, and SAY SO in the effing description.
"But I don't want to turn off readers who wouldn't be into that!" Honey, YES, YOU DO. Because when your description is accurate, you're SUPPOSED to turn off some audiences while drawing in other audiences. Besides the fact that I can't fathom why you would want someone who doesn't like the type of book you wrote to read your book, that's the point of publishing a book and marketing it. Are authors capable of writing books that are legitimately for everyone? Sure, they are. But I would say those books are fewer and farther between and if you haven't written one of those, that does not make your book lesser or weaker. It could mean that you wrote a romance that the romance audience goes absolutely feral for. (Not the ones I stopped reading, but I digress.)
Diana Gabaldon's first book of the Outlander series, Outlander, has a main genre of "historical romance"—or first "historical fiction" and then "romance." It's a lovely piece of media with an overarching plot of Claire and Jamie falling in love with an ever-prevalent environment of the danger they face together and the mystery of how Claire will return to her own time. Outside of just objectively being a well-written, good book, readers loved it because it was exactly what they were looking for.
If you're unsure of the genre you've written—and I can't stress this enough—you should have folks read your work (ARC or beta is great) and give you honest feedback on a number of things, including the genre that came across to them. Don't just give it to your friends and family, and don't just give it to people who don't read. You need feedback from unbiased, well-read readers. Another method, if you're not sure of your genre, is look at it mathematically. While editing your book, consider the number of pages you spend talking about or in X and the number of pages you spend talking about or in Y. If there is a clear winner in one category over the other, nine times out of ten, that is probably the genre of your book and how you should categorize it and market it.
And if this hits home and rubs you the wrong way because you're opposed to having written a romance and set out to write a fantasy. Well. Sorry. Change your marketing, description, and Amazon listing or suffer the wrath of readers you misled and whose time and money you wasted. Shrug.