Understanding genre and subgenre is important, because it gives you the knowledge you need to craft and defy readers’ expectations in ways that work. You need to use this same understanding when you craft your marketing messages.
In the trailers I analyzed earlier this week Star-Crossed created the expectation of a science fiction television show with romance as the sub-genre. The episodes aired thus far deliver a romantic television show with science fiction as the sub-genre. Some of the viewers will be disappointed enough by this defiance of their expectations to stop watching the show, because their expectations were not properly shaped and fulfilled.
The point isn’t that it’s terrible to have a show that puts romance over science fiction. That’s a genre/sub-genre combination that does sell. Just like Twilight sold, even though it put romance over fantasy.
The point is that when you promise one thing and deliver something else, you risk missing the target audience you want (the one that likes what you’re going to deliver) AND alienating the target audience you attract (the one that prefers what you actually promised). You’re only hope is that enough people will be satisfied with the “substitute” and will recruit more of the target audience you really wanted.
That tactic is a bit too risky for my blood. I’d rather create the expectations I’m going to fulfill by promising what I’ll deliver and getting the right audience the first time around.