I overheard a dealer complaining to the show promoter about the people reeking of pot and wanting to handle the firearms on his tables.
He had to keep telling those people to leave his tables and explained that he wasn't legally able (by Federal law) to sell them a firearm.
I have read the ATF guidance (an open letter to dealers published in 2011)
https://www.atf.gov/firearms/docs/op...cinal-purposes
Here is a bit more about the subject:
https://www.thecannabist.co/2016/11/...gun-ban/68075/
Richard