I think reputation and online presence go hand-in-hand. In this day and age if the production house is not posting work on social media (Youtube, Instragram, Vine, Vimeo and their own website) maybe stay clear.

Also pick a company that is aligned to your goal. Do you want creative control or are you willing to let them handle it? Many creative agencies that are top producers will want the ability to develop their own concept.

However, if you have a specific concept and script and actors in mind you need to go with an agency that is setup more for shooting and editing.

I would say that recommendations are always key (at least when they come from people you trust). Online reviews are helpful, but I would prioritize a recommendation from a trusted business partner or client first. Always review the website and content of previous videos (even when recommended to ensure they align with your goals as well).