All I can suggest chalking it up to would be, as my father would have said...
"Faliure of someone else to see the same value in it that you do."
Nothing wrong with that- you just have to either
A. Find someone that agrees with you on your assessment of the the value and wants to put that much "value" in it.
Or.
B. Finding that your value is more than anyone else's value of the product, adjust pricing accordingly.
I haven't seen 88's typically bringing that much money, unless they are pre-64 and nearly perfect. My first question would be, "Where's the box?"
(Different area down here anyway, I have a friend that paid $750.00 for a Winchester 37, 16ga NIB. Go figure. But then again, that's his specialty.)
I'd suggest placing it on Gunbroker and save the $9.00 admission fee into the gunshow, tired feet, overpriced "heart attack" bratwursts and drinks, everyone "fingering" it, and get the full amount possible.
I honestly don't think it is typically possible to get the highest rate something would go for at a gunshow. It can and does happen, but it's "luck of the draw."
The only reason to go to a gunshow is for the fun of it, and not expect to sell anything- at least, that's the way I look at it, but I don't have to make a living at it either, nor would I!