I went to one of these a few years ago. If you were a nurse or medical tech they had real openings. Most of the rest of them were for selling insurance or annuities or for telephone sales. And there were some temp agencies taking names.
One table was for Teleperformance, which was a company who had a call in center for Comcast TV and high speed internet. I interviewed, took the test and they offered me a job in the High Speed Internet Dept. The pay was awful, the hours were late night or overnight and the job meant sitting in a cubicle on the phone with a headset. The high speed internet dept. was half underground and everyone looked just miserable.
I went through the process just to see how far I could get. Reading online reviews from employees (and ex-employees) was pretty grim. I wasn't that desperate for a job and said no thank you. About a year later they closed that call-in location and everyone lost their jobs.
One positive thing at the job fair was that there were people who would critique your resume and offer advice. They had samples and templates that you could take with you. Interesting that when you are over 50 they advise that you NOT put the year in when you list your job experiences or dates of graduation. That seemed silly, it's not hard to tell how old you are.
This was in Sept 2008, before things got really awful in the local economy.
Married, both 61. DH retired June, 2010. I have a pleasant little part time job.