Finding an expert Android mobile app developer can be tricky. There are a lot of things that you must keep in mind before finalizing someone. You may approach a professional company to develop your app or a freelancer working alone or with a team.
If you need a business app, then you should find someone with experience in developing such apps. Similarly, if you are looking for someone to make a gaming app or AR app, you should look for someone who has expertise in that field.
You can tell if an app developer is an expert just by talking to them. With an expert, you will not have to explain everything. They will be able to draw a rough sketch in their minds after listening to your idea and requirements. In fact, they will also give you some ideas about what can be done to the app to improve the user experience.