Looking ahead as I plan on selling my app for a small price, I have a few questions. I know there is a $25 fee to sell apps on Google Play or Google App store, but is that a one time charge or yearly? Is it common practice to pay the fee to get in the system while developing your app or do you have to have the app ready to sell when you sign up? I am mainly curious and need to know a few related things like how do you allow a customer of your app to update the app without buying it again? Does Google's interface or store take care of most of the work and you receive a check every month? Should I join now to see what is there as long as I plan on a released app in the future?