Many large events have a vendor on-site hawking their wares. Those vendors occupy space, of course. Do you charge the vendor for space, collect a percentage of their sales, give them the space free or what? If you respond, please indicate whether the event is a primarily scholastic event or an event open to all.
A “per player fee” is the route taken at the Tim Just Winter Open (Open to all) and the Illinois Opens (open to all) that I have been involved with. The book room is rent free. It is tough for book sellers. Players come in and inspect the inventory then go on-line to try and get the item(s) for a reduced price.
The other route I’ve sometimes seen is a percentage of their gross. That percentage is a smallish number. Less risk for the vendor, more for the organizer if the organizer was counting on the revenue.