If you want to sell stuff for a living, job fairs are job search nirvana. Retail sales. Insurance sales. Financial services sales. Manufacturing sales. If you want sales, you will definitely find it here. For the rest of you, job fairs will drive you crazy. Why so many sales jobs? Because most people who are in sales are not in sales by design. People don't typically go to college with the intent of becoming an insurance salesperson. At the same time, these companies rely on an efficient sales force to generate a profit. Most of them like to "grow their own," so entry level is often ideal. These companies are out there beating the bushes at the job fairs. Quite often you will see a "top-tier" company on the list of employers recruiting at the job fair, yet arrive to find they are only looking for marketing reps (i.e., sales reps).
But here is the key: even if companies are actively recruiting only for sales, if the line is not too long (and you have the time), approach them to inquire about whom to contact for a position in your field within the company. They might offer instead to take your resume and get back to you (in which case you will likely never hear from them again), in which case you should request their business card for direct follow-up, then call directly at a later date to find out the name and title of the primary contact within the company who is responsible for hiring in your line of work.
Don't let the "Sales Reps Only Need Apply" sign turn you away from an employer you are truly interested in!