Hiring freelancers

I have some ideas for apps, unfortunately I can’t develop as of yet, I’m still learning. I would like to get my apps developed so I start my app-preneur journey.
My question is, can freelancers on Fiverr be trusted? Secondly, what’s other freelance websites are reliable, affordable and convenient?
Additionally, what is a must-do requirement when working with online freelancers?
Thank you.