Health fairs are an economical method to get health information out to the public. More people can be reached at once. Fewer professionals are required to staff the fair. Messages going out are more consistent and the professionals sending out the messages are right there to answer questions. Its like this website; mass media but individualized all at the same time, and the “experts” are guaranteed to be just that.
As with everything there is a caution. Be aware of who is putting the fair on. If it is put on by people who expect to profit substantially from your purchases and promote them whether in your best interest or not, be very circumspect. This tactic is acceptable for “home and garden” type fairs, for example, where you know people are trying to sell you items and services that you may want. You might end up wasting your money on a garden gnome you didn't need but when it comes to your health, it may not be just your money you are wasting. It is possible to cause yourself harm unknowingly.
So enjoy the health fairs but be a wise consumer.