I've often wondered how much money these kinds of sales actually generate. I've been to a few sales - sometimes there's some interesting stuff that people just don't want any more, and sometimes it looks like someone is just trying to salvage a handful of change by selling stuff that would probably be better thrown away. For me I don't have to think "I've thrown away nicer stuff than this" very many times before I lose interest in the sale completely.
If you've got decent stuff that's worth having, if you can make it look nice I that's half the battle (at least if you're trying to appeal to buyers who think like I do). If you've got random stuff piled on tables with no particular order to anything you lower the tone of the sale.
I think of an antique market I visited a while back. It was a cooperative, so they had stuff from lots of different sellers all under one roof. Some of what they had was nice stuff, things I'd buy if I had space for them. But seeing a couple of old CRT monitors (yes, the big heavy ones) marked "$5 FIRM" made that seller's area look junky. You can't give that junk away these days, and seriously expecting someone to pay without even being willing to negotiate smacked of desperation. On top of that, the upstairs floor is visibly just sheets of plywood with no attempt to make it look professional, and the whole lot wobbles if you walk on it. Not in the sense that makes me think I'll fall through the floor, but in a sense that they've cheaped out every which way possible while still expecting me to pay top dollar for the stuff there. I compare that place to a gift shop nearby that closed down - their stuff in many ways wasn't as nice but the shop felt homely, relaxing, a nice place to be. It was the sort of place it felt comfortable to stand and browse, where the antique market felt cold and unwelcoming.