Before you jump on the video bandwagon for your virtual fairs consider the following (Warren Buffet says "keep it simple" so I will try to keep this post simple).
Dress Code and Standards: If all participants, attendees as well as exhibitors are video-enabled, set some guidelines for the virtual fair, or you risk damaging your event's brand. If you think that is hard to control, you are right. I just want you to be aware of the risks, and weigh it against the level of usage and the utility. If your audience pushes for it, by all means relax your rules.
Fear of Bias: If job candidates in a virtual job fair have the power to use videos, be prepared to disable that capability to manage the "potential Equal Employment Opportunity concerns" of your Virtual Job Fair organizers, as someone diplomatically phrased it. On why video resumes may not realize their potential, read this article and accompanying reader-comments on the Freakonomics blog titled 'Why isn't the Video Resume more popular?'. It is a different story if a hiring company is using video to showcase why they are one of the best companies to work for.
Training: Consider offering your virtual event participants some training on how to present themselves on video. Offer advice on the best equipment out there. Teach them how to look into the camera as if they are looking into the eyes of the audience, and not squint or let their eyes stray. Make sure that the webcam or video camera is positioned so that they do not look distorted like images through a fish-eye lens.
Going Pro: For pre-recorded videos, try to introduce some standards to the process of recording the videos. If helpful, give all participants a list of questions to answer or address while they introduce themselves on the video. Consider recommending local videographers who can follow your event-standards, so that your members (in the case of non-profits) or participants can simply walk into a studio (or receive the videographer in their offices) and have their videos professionally done, and delivered to them effortlessly at pre-determined rates.
All or none: If some participants are on video-chat, while the others are not using a webcam or a video camera, do not stigmatize those who aren't. Maybe they are just not comfortable. Know that it could be a bumpy experience if that is the case.
Keep costs down: Offering video capability in a virtual fair is no justification for being charged a high fee. The internet allows you flexibility, so leverage that and keep costs down.
Keep it short: Have a compelling story to tell or keep videos down to 30 seconds. Encourage creative use of the medium to show participants your manufacturing facility, your team members, your customers, something to make your company or yourself remembered.
To wrap up, here is a clip about Video Resumes from John Stewart's The Daily Show that you might enjoy!