We are gonna try to do the swap meet for the very first time this year, is there any like pro tips that anyone can share before we go? We literally have never sold anything before. Not even to a garage sale.
Bring plenty of change! Depending on how much you're selling stuff for, make sure to have some quarters and lots of ones and fives. It's good to have a variety of change, but make sure to have lots of small change. Expect many people to pay in 20's even for small stuff. Don't miss a sale by not having proper change right away!
Definitely figure out how to transport everything ahead of time. They do not allow dollies but you can use suitcases with wheels for easier transport. Last year I made the mistake of bringing too much without any help but was lucky and had some nice people in line who watched my stuff while I made a second run to my car. Remember you're going to have to bring back anything you do not sell!
Price tags take a long time to put on stuff (even those pre-priced stickers), so most people just lay stuff out and let people ask how much specific things are. This also makes it easier if you want to knock down some prices as the night goes on if something isn't selling well and you really want to get rid of it.
It's good to bring a blanket or tarp of some sort to keep stuff directly off the ground, but try and use a solid color as patterned blankets can make it difficult for buyers to see everything on your spot if you have a lot of small things bunched together.
Bring chairs! As long as you're not using them to display items, you're welcome to bring chairs to sit in. You'll want this as swap meet lasts a number of hours and no chairs are provided, and you don't want to sit on the concrete that long.
Try and think of the type of people attending swap meet when deciding what items to bring. Sometimes things that would sell well at a garage sale won't sell very well at an anime convention (ie appliances, tools, etc)
Bring water and snacks! It can get warm even in the huge hall, at least after setting everything up I do lol. Especially if you're selling alone, you don't want to leave your stuff to go get food, water, or go to the bathroom. So make sure to do that last one right before you get there!
If you don't know how much to sell something for, do some research beforehand! I often check what things I have are selling for on ebay and price them 5-10 bucks under that to entice people to buy them from me rather than online. Remember most people are looking for cheap deals, but don't be afraid to stand your ground on prices! Unless you really just want to get rid of stuff and don't care about how much money you make, stay steady on your determined prices even if people don't seem interested right away. If the night goes on and it still seems like no one is interested in the item for that price, then you could consider lowering it if you want to get rid of it. Otherwise just sell it online afterward.
COME EARLY TO CHECK IN! There is always a long line that doesn't always move very fast, and spots are given out first come first serve, so if you want a spot near the front, get in line an hour or two early. People start lining up super early, and remember you need to have everything you're selling with you when you check in, so you need to push it all along the line with you! (Also a good reason to bring chairs and food/water for waiting in line).
I don't know if people will try this in person but don't accept personal checks from people. It's often a scam and you won't know if it is or not until you try and cash the check. (I just got someone trying to scam me on craigslist with this old trick so I don't want anyone to fall for it lately)
It can also be handy, if you have time and effort and/or care, to keep a list of what you sell and for how much to keep track of your money. Always keep your money within eye sight or on your person. Unfortunately there are bad people out there, so protect yourself with a fanny pack or something akin so you always know where your money is, especially when doing multiple sales at once or if you need to move from your chair to show a buyer something.
If you have a bunch of one type of item (ie dvds, games, cds etc) it can be helpful to have them organized in some way relevant to the type of item or lay them all out so buyers can see the covers clearly. Some people are fine with digging through boxes/binders for things like trading cards and the like, but many don't turn a second glance when they can't see right away what you have to offer. Everything you can display fully, do so! The easier it is for buyers to see something they want, the more sales you will make. But keep in mind Swap Meet does not allow stands of any kind to display things (except peg boards laid flat on the ground).
Good luck and have fun!