In promoting numerous books over the years, here are a couple things that I've learned that "are what they are," so to speak.
If the tipping point never arrives ... it just doesn't arrive and dumping more money and resources will not change that situation. I compare this to survey. If you survey 100 people and come up with an answer that is perhaps between 10-12 percent it doesn't matter if you survey another 1,000 people, your answer will still roughly be 10-12 percent. So if you're marketing and your book finally finds its place in the market and starts selling, it will continue to sell if you continue to promote. If you're marketing and your book has gotten 10 reviews with no momentum it's not very likely 20 reviews will be any different. The buying mood, the topic or story isn't resonating for whatever reason in the marketplace. When I have a book that has received more reviews than we can count and yet still sales remain overall flat (even if it's the critic's darling) chances are its sales will remain flat and no amount of dumping of resources, time and energy will change it. I'm always brutally honest, and I have zero desire to sell more services when this happens. Disappointment has a name, and it gets assigned to my company when authors feel frustrated and don't understand it wasn't due to our lack of effort -- the market is what the market is.
Can't please all of the readers all of the time. Let's just face the flat-fact that can send some authors into crying jags of protest and self-flagellation: you've put your work out there for critique. Sooner or later someone (there is always a hater for ALL the lovers) is going to say something negative about your "baby". Yes, it's going to zing, pow, ow when you hear it, but it's par for the course. I always encourage authors to focus on the 30 great reviews and ignore the one (and often loud) bad mouth. We've had books like Vengeance is Now where the reviewers went ga-ga and yet one cranky old dude decided to give it a nice slam on Amazon. Even placing as a finalist in the Indie Book Awards did nothing to assuage cranky's complaints. So you just have to know a bad review or just a person in a bad mood when they read your perfectly well written book doesn't mean your book is any less great. Just don't buy the cranky old dude's bad mood as true.