It can be easily detected whether an app was installed through the Play Store, and an appropriate action taken, if one were so inclined. I don't submit my app to 3rd party app stores, but I do allow it to run if it was installed through one, or through sideloading. I don't mind the Chinese using the app, probably the biggest market where Play Store is not available.
What I don't allow are reverse-engineered copies of my app, recognizable because they're not signed with my developer certificate. Those mostly ripped the app part, added something to the layout that display ads, and put it back together. That's an immediate termination :-)