It honestly depends on the artist as cliche as that seems.
When Stan Lee was alive it made more sense to shop on eBay given the price of a Stan Lee signature and the style of his autograph. His autograph had started to become more and more of a blemish than a signature over the past five years. So if you wanted a decent signature with decent placement you had the option of rolling the dice and doing it in person OR finding the book you wanted with the signature placement and condition that you desired for in many cases less than it would have cost you to put that whole package together yourself.
Artists like Skottie Young have drastically increased their prices for any books going to CGC. Okay then, what that does is in effect completely turn me away from your table. When the artists jack up the prices I fear it has a negative impact on the long term.
Skottie Young and Neal Adams raised their prices which means I do not even approach Skottie Young's table anymore.
Someone like Larry Hama is a cheap autograph. I go to Larry Hama, get a free signature, I buy a sketch if I am early on the list and then I wind up buying a couple of other things while I am at his table.