I used to be part of a few groups for this stuff. It usually worked out pretty well with game console meets. Everybody could bring their bins of stuff, folks would do their trading, and people not actively trading would be off on the side competing in some little tournament. Generally a laid back event.
The arcade/pinball based swap meets I have attended have not been as good. Lots of dudes who seem to be ethically challenged, mostly available items that are crap because it's so much harder to bring coinop stuff anywhere, and not nearly as social. Arcade stuff is good for gaming gatherings but not so good for central swap meets.
My experience has largely been the same but I feel it's more regional.
I lived near Reno, NV and spent an inordinate amount of time going to all sorts of swaps. CCG, Comics, Consoles, toys, movies, music whatever (except arcade or pin). Unless the ---uvula--- from Hit-N-Rip (Imagine a cross between the Simpsons Comic Book Guy and the :censored:tard from NGF) was at one of them, the gathering usually went very well. If we wanted to BST, we would be off in our own area doing our thing. If we were there to play games or whatever it may be, we would keep to ourselves in another part of the floor. Anyone who tried that bull ---steaming pile of meadow muffin--- "high pressure" sale or trade crap on the game floor would be met with a swift boot to the ass. Very comfortable and friendly, especially for those who are just getting into the hobby.
I moved to a different city and the sub-culture was very different. WotC just started their ranking system the previous year so if you didn't have your card, you couldn't play. Not even during non-tournament games. I was already carded but I felt super bad for those really young kids just learning the game. In that same vein, nearly every gathering had tons of Comic Book Guys or a NGF :censored:tards. If you couldn't cite the exact chemical composition of the purple ink used in Green Lantern #4 and the exact number of words uttered in page 6 panel 4 or knew the exact number of MTG Anson Maddocks illustrated, in what sets and their rarities. You would be scoffed at and your trades would automatically be devalued by 20% (I wish I was kidding). The ---That which is odiferous and causeth plants to grow--- got so bad I learned the meet schedules just to avoid them.
That was about ten years ago when I finally flat out quit. The sub-culture seems to be improving though as a ComiCon just finished this weekend and I've heard positive things about it regarding the people there.