Most conventions aren't even comic cons anymore, they are all turning into pop culture cons, while 90% of the tickets being bought up cosplayers who have no interest in buying comics, instead they buy the t-shirts, action figures, posters, prints.
Comic dealers are left with "How can I make money at these cons if I only sell comics?"
You'll have to adapt.
Expand your inventory to what people at the show actually buy. (start carrying other products that aren't comics)
If you don't want to do that. Alternative is to mainly sell comics online.
Otherwise, you'll be sitting at your $3,000 table, bored to death.