At the CC-AWA's Annual Conference held in Charlotte NC each year, the main (and really the only) rule we have is that the flea market does not start until 8AM on Friday morning. We call this our "LeMans Start".
This is a take off on the old tradition in Formula One racing where the drivers lined up across the track from their cars and at the start of the race they sprinted across the track, jumped into their cars and speed away.
Vendors are allowed to park their cars in the flea market parking lot starting on Thursday, they can set out tables to help them claim their paid for spaces, but they are not allowed to buy, sell, trade or display merchandise until 8AM Friday morning. To help with enforcement of this rule, everyone must be out of the flea market area and outside the main entrance before the start at 8AM.
We created this rule in an effort to stop the progressively earlier and earlier starts every year. It helps make it much more fair for those that have to travel to get there on Friday morning.