Hiring a mobile app developer can be the toughest thing, as its an expensive affair not just in terms of money but also time. Wrong selection can ruin your project and the time you have wasted and can leave you frustrated.
Hiring the right is not just about finding the technical problem but also other factors like the vibe, attitude, aptitude, communication, logical reasoning and more importantly the willing to solve a problem attitude. All of this cannot be taught while hiring but can be evaluated.
What you really need is an understanding of the process of the mobile app development company so that you have an idea of each step and stage and how long will it take to finish your app and accordingly, you can put a clause of penalty if not done in the given time.