I went to I-Con 26 in New York this year as a guest to promote my web comic and I noticed every web comic artist there was pushing to get commissions (some were very pushy and rude about it). I was wondering how important getting commissions are for you who attend conventions, and how do you decide on what to charge?
Well, it's nice to get them, of course. I wouldn't rate them as so important that I would ever become pushy or rude about it, though, lol. I usually just have a little sign up that says "Sketches $5" or whatever price I'm charging that paricular day and will occasionally offer one to people if they seem interested in my art.
Commissions kinda depend on how badly you need the money too. I usually do small commissions on a donation basis. A lot of people like to come around with a sketch book and just get whatever drawings they can from artist alley attendees. If they really like what you've done it's not unheard of for them to drop you anything from a $5 to a $20.
I'd say unless someone is asking for hours of your time, give 'em a free sketch and make sure to sign it and put down your web address. A new reader is worth more than money! ^_^