I have an app that has been a consistent performer and has given me stable revenues (in 7 figures annually) for the previous 4 years. I am only a developer and never do sales & marketing, only focus on development. There is a sure shot possibility of increasing revenues by 2x-3x with proper branding & marketing. Either someone buys this app from me or I get a partner with the right skills so that revenues increase 3x. Anything is okay with me.
There are many websites where you can sell your app!
The best place is on www.fiverr.com, auction type of selling!
Make Money By Selling Your App Code Work
You can become an author and start selling your iOS and Android Templates to a huge group of interested people. You can build a Business by Licensing your App Templates, Game Source Code and Components.
About marketing and increasing downloads in app stores send me the link to the app so I check it out.
I do great ASO!