1. They Have Experience in the Type of Content You Need
(We'll assume everyone knows to look for an ad agency to make online video ads for them.) If you need Editorial Videos then find a company that understands what works in this kind of video. Not just any old production company will do. Same for Entertainment--whether one-off or series)--you need someone with a track record of success here.
2. They Understand Online Video Production
Those that have worked in television for years and years tend to think about digital in a certain way. The same holds true for companies that have worked in film or large commercial projects. You want a partner who understands the uniqueness of the online medium--and how it is evolving from the desktop/laptop world to the tablet/smartphone one.
3. They Are Sound in Strategy and Execution
What you are looking for is a thought-partner in addition to an execution partner. Can they help you think through your strategy for your online video mix, and then can they help you get those videos produced? Or if you feel like your strategy is all shored up, then you'll need someone who gets and can work within the parameters of that strategy. Video content marketing is new and powerful, but not everyone saying they do it really knows how. Ask for examples before you get started.
4. They Pre-Wire Your Content to Perform in Search
We've said that Google is the homepage of the web, so getting your content high in rankings is key. You want a partner who knows the right topics and can develop scripts that will perform well for you. Not all topics are searched equally. So, ask about their topic and script development process.
5. They Get Talent in Front of and Behind the Camera
Creating content is talent plus craft. Make sure your partner is putting talented people in front of the camera for you--real experts who know their material or talented performers. But you also want talent behind the camera writing great scripts, directing, shooting, producing, etc. It is not easy making good video and having a great camera doesn't make a great video.