If someone comes to you with a project, and there's a chance you won't be able to get to it in time - DON'T TAKE THE PROJECT. If some unavoidable shit comes up, let the client know early on, maybe send your overflow to another printer. DON'T tell them at the last second you can't print it when 3 weeks earlier you made an agreement to do it quickly.
This is the second printer in a row I've been burned by, I'm starting to get a pretty negative view of the industry. I'm to the point where I think I'd be better off learning to print myself. It makes me look bad when the show comes up and the posters I promised aren't there, not to mention the days wasted designing the thing.
Screenprinters - if a new client comes along, treat them well - they may end up giving you a ton of repeat business or recommend their friends.