Apps offering free data or money based on using and sharing
Your concerns are 100% valid!

A few things you can consider while making a decision whether to install such apps:

-Firstly, do you really need this so called app? If not, don't install!

-Secondly, see if the app has any good/social cause which really helps people if you download the app (when i say help, i dont mean your friends getting free money), if it does, then consider helping out!

-Lastly, if you do choose to install the app, check the permissions the app is asking before installing. Try not to download from unknown sources, and do read the reviews. If you have Xiaomi phone or cyanogenmod/lineage, they usually have 'App Permissions' sections, make sure not to give the application any permissions!