A friend of mine is wrangling a vendors for a convention for the first time, and he's asked for our input on a few things, knowing that we've run the Dealer's Room for DucKon in the past, and are denizens of such a room. Here's some things to keep in mind if you're ever in that situation, especially if you've never been behind the tables:
Leave space behind the tables for vendors to work, as well as for the customers. 8' wide or more aisles for customers is not excessive, especially if there will be ladies in large skirts or anybody in bulky-ish costumes.
If there is a door in the room that must remain accessible as a fire exit, you'll make keeping it clear somewhat easier by not putting any of your vendors in front of it. You'll still have to check regularly to make sure it hasn't been blocked, but it won't be quite as bad.
Remember that you're writing the rules/guidelines for the 10% of the vendors who will try to push said rules, not so much the 90%, who learned how to play nice with others in kindegarten.
Even the kindegarten graduates will nudge the boundaries.
Every region has one or a few vendors that make the room wranglers' jobs difficult. It will make your life easier if you can talk to people who have done the job before and warn you who to watch out for and why. Problem vendors can be very charming to customers, and even to you while making your life difficult.
If you put tape on the floor to delineate the limits for one vendor, you have to do it for all the spaces in the room.
Patrol the room regularly. There may be issues that come up that aren't serious enough to send vendors away from their tables to talk to you about, but will come up if you check in as you're going around the room.
Keep an eye out for creeping displays when making rounds, and chase them back within bounds firmly. Vendors can sense waffling the way predators sense fear.
No matter what you do, someone will complain.
View From a Hotel Window, 4/28/17: Southfield, MI
15 hours ago