@dsavior
No, I don't promote my books in a special way. I just have a fb site and an email list for my best selling fiction and non fiction pen name. But my other (6) pen names have nothing. I think the best way to sell more (even the older books) is to publish constantly more and more books. Because then you are always listed in the "new releases list "= people will buy your older books if they like you actual book.
On the other hand: My erotica book sells good although my pen name is completely new and it has no reviews. I don't know why. I'll try to make everything perfect. Perfect analysis of the niche + keywords, perfect cover, perfect description etc.. I do everything as perfect as I can. I also spend much work for the "look inside feaure" to differ me from other competitors and to catch the readers. Eg. My main headline on the first page is no boring standard text but a nice looking graphic followed by a graphic of my pen name (it looks like my pen name is written by hand or a signature - that's more personal than just a text with a standard typo. Then I have a catchy foreword and also a nice banner of my whole series with 3D boxes and mirror effects - so it looks really professional. I also include a yellow/blue "order button" directly under this ad banner. And so on. I think people are bored of the typical looking ebooks. They've already seen that hundred of times. But when they look inside my books and see the colorful graphics and stuff like that ...for some people it's like: "Loook look, he made fire!!!" Lol And if you get the attention you will sell. Search for the "AIDA formula" on Google. It's a basic marketing method that works for EVERY product. And you can also use it for your product description. Don't use standard phrases that everyone is using. Be creative!
Hmm, I've also made bad experiences with other writers when I tried to outsource. Bad qualty, not delivered, they just wanted to steal my niche ideas, and so on and so on.

There are a lot of crazy people out there and it's not easy to find a few good writers.