Turns out, the guys who show up at your yard sale 30 minutes before the advertised starting time and try to offer about half the posted value of items are there because they know what they can resell for a good price.
I'm not saying don't sell to them, but definitely don't take their opening offer.
@Satsuma Yeah, these are the guys that treat it like a job. (I mean, I think it's their side-hustle, but they definitely are doing it like it's a job.)