As a freelancer, you have to be ready to jump at any opportunity. I keep my tabling supplies in my car at all times, and when I go to a local con as an attendee, I sometimes check to see if anyone backed out on a table. It's worked a few times, but I'd exercise caution before trying it. Some cons don't take kindly to tablers that subvert the normal order of things.
I'm also working on getting my setup and tear-down system fine-tuned. I've got setup down to 45 minutes and tear-down at around 30. It's much faster if I'm at a con where I'm not pushing prints and don't have to set up my rack display.
For the entire run, please visit www.CosPainComic.com!