delivered a video project with similar budgetary or creative requirements. If they have, they should be able to provide evidence of this, including video samples.
Every video production project is completely different, so it is unlikely you will find a company who has worked on something exactly the same as yours, but if they have worked in the same or a similar industry, it is likely they will be able to really understand your requirements and the commercial environment you are operating in.
Location / Facilities
Some video production companies will have a great looking website, but they could very well be a one-man-band operating out of his or her bedroom, with a semi-professional or second hand video camera, pulling the film together with a free piece of editing software. That is not to say there are not any talented people out there