I know that this is a difficult question to answer, but it's an important one to many artists that go to conventions and sell art
Not all conventions are the same in cost prices for seats, but in NZ, I know that a 'collectors stall' at Armageddon costs around $280NZD for Auckland Armageddon, Doujin overload costs about $30 for a 1 day stall, and Inkforge costs about $15. Big conventions can have VERY costly stall, but theoretically the popularity of the convention should mean that the artist purchasing space at the convention should have an easy time making up for their stall an printing costs.
This I know isn't the case in New Zealand.
So, what I'd like to know is what you guys like to see. I'm not asking what fandoms you specifically purchase cause that'll be different every year, but when you go there, is something that makes you want to purchase an item? What's the seller for you?
Price- Do you hit a stop sign if something costs more than a certain price at a convention? I'm not talking of good deals here, and I'm not talking official merchandise. Will you actually be stopped from buying something if it's a certain price or higher? What is that price?
Quality- Do you only purchase art if it's inspirational / high quality even if the cost is high? When I say quality, I don't just mean only quality fanart. I mean quality ANYTHING. Original characters included.
Original traditional art- Do you buy one of art? I don't mean doodle originals, but full fledged traditional art. Colour or not. Stuff that (SHOULD) go for more than $20.
Large prints- Prints seem popular in NZ, but what do you want in a print? Do you only want fanart? Do you want a piece of art to hang on your wall? What do you look for in prints?
Content matter- What content do you want to see in art you purchase. I'm not asking about special case stuff here- are you more interested in fanart only, Original characters only, stuff with LOTS of colour, something that is cute, has girls, boys, yaoi, yuri, het... what content makes you want to purchase it? (And don't say anything please, cause this isn't true. People are very rarely interested in seeing a wide range of art- artists included. We all have interests)
Other merchandise- What BESIDES prints and single sheet art do you like to see? Art books? Comics? etc... and what do you want out of them. Anything specific that catches your eye?
Art style- Does this matter to you? If yes, then how much so?
Artist layout / attitude- When you go to a convention, do you want to zoom past art that doesn't interest you and stop at ones that do? Or do you want to talk to all the friendly looking artists, and fish through thier stall of art you can only look at? Do you like to see all of their products at once, or have an 'experience' with interacting with the artist?
On the spot commissions- What do you want in an ont the spot commission. Colour only? Specific mediums? To be able to get OCs drawn? What? Do you want on the spot commissions at all? (This doesn't include dirt cheap ones which obviously you wouldn't think twice about getting)
Adversing Will advertising an expensive product pre convention make you more likely to want to by it, like a $100 painting or something?
None of the above / something else Sometimes people don't go to cons to buy stuff. What'll attract you to my stand anyway? Or if I've missed something out, tell me, and I'll add it

I'm aware that con goes want to have their own unique experience, and over the years, I've noticed that no two con goers take the same from a convention that another wants, and that the audience at any given con is different. I know I and many other artists REALLY want to hear this feed back though cause it's SO hard to cater for someone else's tastes.
I look forward to everyone's responces