I will tell you one thing: Don't download apps that promise a lot of money, for low effort, in a short period of time! For example, I tried many apps that allowed me to watch 15 to 60 seconds ads, earning 50 cents for 20 videos. Once you reach $100 you could cash out with a giftcard for Paypal, Steam, Google Play, and what not. I used to be able to gather $3 to $3,50 an hour per device, constantly opening video ads. Not having a job at the time, I could do this all day, and earn about $45 on a day.
However, when I tried cashing out, they said I needed to wait a few days. At one point, my reward had a green text saying "succeeded", but I haven't received anything. I tried contacting the developers of the apps, but no response. Thus, I've wasted many hours, and some extra money needed to charge my phone.
Always read the comments of an apps before starting it. Don't just look at the rating, the first 3 comments on most of these apps will tell you when they're fake.
If you're not sure about a money making app, give me a link to the Google page, I should be able to tell you if it's legit or not, without even needing to download it.