People want to know that they are going to get if they pick up this book and pay money to get it and then spend their time to sit and read it. By telling people the genre of the novel, the ones who want to read that genre will pick it up and get it and those who don’t want to read that novel will simply pass by it without a second glance. People don’t want to pick up a book expecting a murder mystery only to find it’s an cringe-worthy, cliché romance between the motorcycle riding-leather jacket wearing bad boy/gang leader and the awkward, shy girl who does nothing but read (even though she doesn’t pick up a book after the first chapter has ended). People want what they pay for. If they pay for the murder mystery, the want the murder mystery. If they pay for the demonic clown that eats children, they want the demonic clown that eats children. Don’t give them the opposite of what they’re looking for.
If you’ve written a romance novel, give it a lovey-dovey title and make the cover at romantic as possible. If you’ve written a murder mystery, give it a suspenseful title and a dark and mysterious cover. Don’t give the novel about the demon terrorizing a town a cover with two people staring lovingly into each other’s eyes and the title that screams “IF YOU LIKE STAR WARS, READ THIS!” It doesn’t work and the readers will be annoyed that they thought they were getting one thing and they got something entirely different.
People want what they payed for.
People want what was advertised.
People want what you promised them.
People do actually judge books by their covers.
Give them what they want.