Are reselling apps a good app to get money? Or not??

I wanna make some money and my friend has given me a great example; a reselling app!
I was really excited about this, but I'm kinda nervous because I don't wanna get scammed, nor have an unhappy costumer, or something bad happens, I also haven't asked my parents and what they think about it yet.
It is a good way to get money, but would this be a safe way to make money/get money, or should I wait for a different type of job??