Selecting a right partner from all, you see on google may be difficult, but there are a few steps, which can certainly let you select a right partner. You should start going through their websites and assess their previous projects. Check if the mobile app development company has really worked on the type of mobile app, which you are looking. 

A professional mobile apps development company, will certainly have their apps listed on the website. You can go ahead and discuss your project with them. If they have a clear approach, the you might be talking to a right app developer.

Check their apps portfolio and go through the projects in detail. Check the links for native and cross platform apps and download on your phone. Check their workability and UIs.If you are satisfied, you can proceed with discussion. 

Select a mobile apps developer only if company can provide you ongoing support for various releases. They must be able to handle bugs quickly.
Before giving the mobile app development contract, get code samples and review it at your end.

If the code has clear indentation, you are at the right place. Pricing can be a criteria but cant be a final decisive parameter. You may not get a perfect thing, dirt cheap. Choose a mobile app development company,successful project, even at little high price