I'll organize these in point form. It's presumed already that the reader knows what they would present at a table at these Cons. I'll point out that it is actually very easy to obtain a table, to meet the requirements and so on; success, quite honestly, is a matter of approach. Consider each, as the reader will; we have done our best to incorporate every one.
1. Learn How to Sell. Being completely honest, this knowledge does not come from me. I have a number of skills but for most of my life, selling hasn't been one of them. My daughter, however, sells like a demon. Out of high school, like most young, slight girls, she dove into the retail business. Long before that, she had gotten involved with trading things on line, seeking out rare items, buying them up and waiting for the right sale. Her early experiences in retail shops expanded upon this for a while, until I thought she would make it her career; then she changed her mind and embraced merchandising as an alternative. For those who don't know, this means window dressing and organizing a shop in order to make customers comfortable and interested enough to buy. It is really just a means of organizing the space so that things are less confusing - and at the same time, encouraging.
I've had a crash course these two years in these things. I let my daughter set up the table, I take her advice on how to talk to interested parties, I smile and concentrate on what people say to me so that I can honestly and appropriately answer their questions, rather than trying to force a spiel on each individual. I open the book, I show it, I put it into your hands - and when the conversation lags a bit, I name the price of the book.
This last is amazing. For most people, this is all they need to hear to "close" the sale. They are already considering the book - but they don't ask the price because it doesn't occur to them. They aren't thinking about price; they are thinking about what it is that interests them. The price, when they hear it, "snaps" them back into the real world and reminds them that they only have to part with money in order to have it. Nine times out of ten, people immediately reach for their pockets when they hear the price.
I've seen dozens of vendors now who won't say the price of what they have. They are ashamed of the price they've chosen. They feel naming the price is pushing too hard. They will sit and mumble about the book for five, ten minutes, until the sale walks away.
If you want to be a vendor, either do it with someone who can sell - and then take their advice like it's gospel - or else go work in retail for six months and get good at it. If you can't get good at it, forget ever being a vendor. In this modern world, that means forgetting that you're an artist or a crafter that people will ever notice. If you can't sell your stuff, NO ONE will ever, ever, ever know who you are.
2. Ensure the Product Has Value. This is not as important as the first point; but if you want to sustain yourself for longer than a single show, the work has to be something people can view again and again, both from day to day during the event and the next time around. I had a lot of people in Edmonton come around just to talk about the books they bought from me last year, giving me an opportunity to press for them to support me on Patreon or to buy into my online classes - which, admittedly, were a hard sell. They require faith, since there's nothing concrete to support the notion that the classes will deliver what they promise - except my presence and what measure of credibility I offer.
We always see vendors who have a product that is, without a doubt, simply sad . . . particularly in Artist Alley. We all remember people who could reasonably draw in school: often this level of drawing is presented as "art" for $10 next to people who are displaying spectacular content at comparable prices.
3. Have a Story. It isn't enough for the work to be comparable or even amazing. My daughter, who has been to more Cons than she can describe (she's a cosplayer), makes this point: "What is it that makes this amazingly fine jewelry better or different from that amazingly fine jewelry over there?" There are artists all over the place and every person only has a set amount of money to spend. Most of them are carefully counting out every purchase because it means if they spend $15 here, they won't be able to spend that money somewhere else. This competition is always there - no matter what anyone is vending. Every book I sell is money out of someone else's pocket - because the buyers are going to spend their $300 or $1,500 or $7,500 on something before the con is over. That is an unquestioned fact.
Many of the buyers, however, know that the vendors have worked and struggled and banged their heads against their crafts long before getting to this point. People want to hear about this struggle. They want to know the reason behind the book, the inspiration behind this magnificent sword for $1,200, the concept underlying this set of figurines, the philosophy that impels this production company. Tell them. Anyone who has gotten to the point where they are selling their work at a Con already has a story.
Mine is simple. No one has ever written a proper academic book for a Dungeon Master who has been playing the game for ten years or more. No one has ever explained what we're doing right when we have a great night running. I didn't know myself before starting to write the book. I had a tremendous moment of inspiration - I realized that the situational awareness of an emergency first responder was applicable to the situational awareness of a DM during a game. It is all a flood of information in and the necessity of making decisions and managing people in a very short period of time. The fact that RPGs are not life threatening is irrelevant. The thinking process is the same. And as I explain this to varying degrees (depending on the listener), I get a tremendous response. I can make it very simple for people who only just grasp the concept of D&D - or I can dive into it as deep as I need for anyone who wants a detailed analysis of my thinking process. I love these people - particularly as their eyes grow wider and wider as I discuss the principles underlying details like capitalization of ability, managing negative responses to medical physio-therapy, pattern recognition, functional design or any of the other disciplines underlying the writing of my book. My story isn't "made up" - it is a straight account of how I got to where I am.
4. Don't Go Alone. This is fairly straight-forward. People try to be vendors without help, because they don't know anyone or they can't afford to pay anyone. It's awful. We need company, we need someone to talk to after an insulting or abusive customer (and we had them), we need grounding, we need mental rest and we need someone to encourage us to remain in a positive state of mind. Seeing people on their own, come mid-second day, it's clear how glum they are, how tired they are, how frustrated they feel if they're not selling or if they've underestimated the resistance to their product. It isn't good.
We don't need someone to help; we just need someone who we can talk to, even if we are doing all the work. If they're doing work too, all the better - but they better have more motivation than, "I'm doing this for that guy." They need a story too, they need to know how to sell too.
5. Go With the Right People. So, a friend of ours, Jim, found himself helping out an artist friend of his, David. David had been lax in his judgment and his booth had six "helpers" - girlfriends of friends and volunteers he accepted because "the more the merrier." After Friday's show, the first day, all of them - including David - got hammered drunk in the hotel room, with two exceptions. Jim and another helper, Brenda, went to manage the table - they were getting paid by getting a cut of the amount sold, so if they wanted any pay at all they had to do something. Saturday started at 10 officially, 9 for the early-passes. Jim and Brenda worked - no one else did. Throughout Saturday, the others filtered to the table, hung over, unhappy, tired and draped all over the chairs around the booth. David, the actual vendor, didn't get there until 3 o'clock.
The horror show didn't get better. As money collected, several of the helpers tried to rob from the cash box, even though it was supposed to be split. This got out of control and tempers flared. Half the booth wasn't speaking to the other half and the Con still had a whole other day. Guess what happened Saturday night? Yep. More drinking, a worse situation, three people not coming in at all the next day and Jim swearing at our table about how he was never, ever, going to do this shit again.
Being a vendor is serious. But stories like the above are going on all the time. Artists, having gotten there, don't care. Helpers come up to "help" and end up taking advantage of the one person who actually cares about their art. Helpers wander off and don't come back for three or four hours. Things go missing. It's really important to ask, "Would I pay my friend an income for what he or she is doing?"
I'm lucky. I have a sensible daughter. It is in the family. I heartily recommend having a child, raising the child to be a human being and then shutting the fuck up as a parent and letting the child run the table. I do this and it works great.
Conclusion. There's a lot more. Displays get built so that it isn't even possible to see the vendor. Vendors spend the whole Con sitting on their ass. There's nothing for the customer to touch. People ignore customers. Not displaying all of their product. Coming in late. Leaving early. Not trying in the last half-hour of the day. Having nothing that identifies the booth. And so on.
The people who make money are those who watch others and avoid. It isn't as important as one might think that the booth be stuffed with AMAZING things. Ours wasn't. But we were memorable because WE were; which is the point. I'm not selling a backdrop, I'm selling me and my book. Many vendors forget that this is the point.