Below is an article from the September 2009 PennsylvaniaJobs.Com Newsletter that reinforces the importance of professionalism and preparation at a job fair.
Strategies for Job Fairs
Job fairs are employers' territory.
With the fair-like atmosphere and so many employers contending for candidates, it would be easy to assume that employers are there for you, and all you have to do is show up. While this is true in a sense, you are there for them too, and you are competing with hundreds-maybe even thousands-of other job seekers. You're essentially in employers' territory, just as you are when you attend interviews at their offices. During interviews, you must leave favorable, lasting impressions in employers' minds, not just résumés in their hands. The same goes for job fairs, but more so. Remember, hundreds of job seekers may have been at the booths before you, and there may be hundreds after. Dress sharp and act professional.
Job fairs are strictly business to employers.
Employers paid big bucks to be there. Even if they have an overabundance of jobs to fill, they are still there to find sharp, qualified employees who have interest, dedication and initiative, and you can't display all that on a résumé alone. To succeed, take job fairs as seriously as employers take interviews. Since they tend to be more casual than formal interviews, you can generally loosen up a little and act more friendly. But body language, manners and other interview professionalisms still count. Read the mood of the employer representative with whom you're talking at the moment, and adjust your professional style accordingly.
Spend some quality time.
While some candidates are trying to win a place in the Guiness World Book of Records for distributing the most résumés at a single career event, you can be smooth talking your way into their ideal jobs. It's much better to spend some quality time talking with only a few, well-targeted employers who are looking for your specific skills, than it is to just toss your résumé at every booth.