You always want to mitigate risk, for you and for investors, or partners. One of the easiest ways is creating fake landing pages of your product idea. You then run ads, fb or Google, and see if people 'convert'. Convert can be giving their email, clicking a button like buy now, faking all the way...
Hard to give specific advice without knowing what the app is. If you’re interested in going down the sales route I can assist as I have sold several apps and developed 100s for clients. On the revenue side, I am assuming your already tried a freemium model with in app purchase as well as ad supp...