It's a hard nut to crack. The 3rd party developers should be a good choice to hire for start-ups when no CTO on board or they are in short of  on-site developers.

On the other hand, outsourcing is not that easy. A huge number of outsourcing companies all over the world and though they are mobile application developers, they all do it in a various way.

You can use a short checklist below to decide your best outsourcing partner.