Thanks for asking this question Frank. I have a similar question along these lines.
While I have not sold any pens at pen shows, I heard many makers selling fountain pens do tuning to the nib when a pen is sold at a show. I am assuming each maker is checking the ink flow and tine alignment first and then polishing last. I have found these three steps can take a considerable amount of time depending on the condition of the nib. I am guessing an experienced pen maker can go through these three steps in 20 minutes (or less if the alignment and ink flow are good) which is a lot of time required if you sell a lot of pens.
My question is how much of this work is done prior to the show. I would assume you want to make sure the ink flow and tine alignment are sufficient prior to the show, and focus on fine tuning the nib (smoothing) at the show, but that could also be a lot of prep work since most makers offer up to six different size nibs for their pens.
As far as inking the pen prior to selling it, I would think dipping would be a better option during the tuning stage.
I am very interested to hear with the others have to say.
Thanks again for the question.