Are you kidding? All people sell at booths like those are bootlegs. Why do you think this should be the line drawn in the sand? That’s the way it’s always been and that’s the way it always will be. Either you’re a noob to conventions or never bothered to check out those types of booths. None of it is official, even if it’s been officially released.
I’ve been to a horror con a few times in recent years, and it’s a mix of legit titles, region free discs of unknown origin, (at least to me) and then bootlegs of films that have never seen a legit release, and workprints. All really depends on the seller.
The bi monthly comic con I used to attend up in L.A. back in the 90’s was the Mos Eisley of bootlegs though. Got my first copy of the Holiday Special there. A smaller local con I attended in 2002 had at least one seller brazen enough to be offering an AOTC VHS bootleg that was probably shot off a theater screen.