FWIW, I contacted NGC today and they will not have on site grading at the Central States Show being held in Schaumburg, IL this April. They will be as a company accepting submissions, but not grading on site.
ANACS and ICG used to give free verbal opinions, I don't know if they do anymore. As a general rule PCGS and NGC do not give opinions and one reason for this is the people you see at the table are NOT the graders. They are simply staff there to handle submissions.
I've dropped off a few pieces at both the PCGS and NGC tables for regular submissions. It just makes sense to avoid the hassles of packing, price of postage, and risks associated with the delivery to either California (PCGS) or Florida (NGC). guy