As a collector, what makes a good card show for me:
1) Variety of products, years, and services that people have for sale or display. It pains me when every single booth sells only the latest Series 1/2 hits at prices on Neptune and calls anything older than one year "junk wax". I like to see boxes, team programs, single cards, game worn memorabilia, museum displays (*cough cough, shameless self plug here), drawboxes, and have other fun things to do at booths.
2) Respectful sellers. I hate it when you tell a booth you like game worn memorabilia, Arturs Irbe, and the Canes (especially living in Edmonton as I do) and they go off on you on a rant about how crappy Archie was as a goalie, how fake every game worn thing is because their buddy said so, and how the Hurricanes are garbage and how weird you are for collecting any of them. *sarcasm*--> I just cannot wait to spend money at your booth jerk. A great conversation about hockey, about life, etc., makes me eager to buy something at a booth, even if it isn't something I need, just as respect for the seller for being a good person.
3) Autograph guests. I never go to a show just for an autograph guest, however, the right guest can keep me around an extra few hours which is hobby code for "oh crap, there goes that extra $200".
4) Price tags on things and organization. More of a nitpick with individual dealers, but organizers could easily enforce the first, is when booths don't have prices on anything and you have to ask them and then they bust out the Beckett guide and quote you Beckett high on everything. If the seller has a price, it is easy to work with them, or at least give you a benchmark for organization. If they do not, I automatically assume they want too much and do not bother. Same thing when their cards are in some kind of organization (GU cards, AU cards, by team, etc.), versus the 500 card vertical pile where "there might be something in there".
5) A ban on non-hobby related booths. I hate when I am looking for my cards when there is one of those "cellphone protection gel", or "back pain cream" booths with the sleezy looking dealers that makes me feel like I am at the middle of West Edmonton Mall with those pushy "mall gypsies" harassing me when I only want to shop.
6) Plenty of space for both moving and browsing. A lot of collectors attend shows and it sucks when you are cramped into a tiny area. It's tough to browse, to be relaxed, move around, and as mentioned in a comment before, bad hygiene can exacerbate the issue. Tight space makes me want to leave quicker since you cannot browse or move in peace, versus a nice open space like the Toronto Expo or Summit where you can step off to the side, where you can browse without thirty people getting overly intimate with you trying to look into the showcase you are also looking at.
As a dealer/museum booth operator, a good show has or is:
1) Great organizers intelligently placing booths in appropriate areas. If all of the wax dealers are set up next to one another and all of the game worn displays are next to one another, it waters it all down and hurts all of their businesses. A good promoter will allocate them appropriately far enough away from each other, thinking of human psychology in how people gain and lose interest throughout the course of a show.
2) Lots of respectful attendees who ask questions and have fun. That's why I am there is to have fun, and sometimes a miserable wanker can take the wind out of the sails right in the first hour when they want to be that smart guy who criticizes everything or looks at you like you defaced his mother's grave after greeting him with a "good morning".
3) Some kind of perk for setting up. Booths are not cheap and it is nice when you are given something like a free autograph ticket, line priority for the guests, or something as it is tough to get away from the booth at times and you also want to experience the show. Heck, even a free meal voucher is nice since you are sitting all day and generally do not have the chance to get away for any reason.
4) Well timed. A show in July (this year possibly excluded as the NHL may resume and still be active then) versus a show in the middle of the playoffs makes a huge difference in attendance which translates to profit earned.
And of course, a lot of the points can go for both categories and I am sure I missed some, but that is how I feel.