The best way to handle vendor no-shows is to prevent them. Collect booth fees upfront so vendors have something on the line, and send a reminder the day before your event. A text reminder works better than email since most people check texts right away.
On event day, give no-shows a 30-minute grace window, then move on. If you have a waitlist, reach out to backup vendors in advance so someone is ready to fill gaps. For repeat no-shows, have a clear policy in your application terms so you can remove them without pushback.