Explain: Buying from artists--"via agent"???

Hello hello,

Question 1:
(a) So, if an artist is being represented 'via agent' does that mean that they are either not present at the convention and/or we cannot speak with them directly there?

(b) I mean, what if you want to commission an artist but first want to explain to them exactly what you want? Does that mean you'd have to write everything down and submit a note to the 'agent' who would then forward your request?

Question 2:
Should we expect any 'via agent' artists to deliver any commissioned artwork via mail? (Assuming of course that my suppositions above are correct.)

Endnote:
I guess I'm looking for someone to elaborate on what I should except at the convention when an artist is listed as 'via agent'

Thanks a bunch!