Well, you couldn't pay me to buy chickens at a swap or auction from anyone, to tell the truth. I never buy started birds from anyone. All are hatched here because of the disease risk-people will ignorantly (or dishonestly) sell you sick birds and you cannot always tell if they're ill just by looking at them.
As far as SLWs at 6 weeks old, sometimes you can spot a cockerel by the comb being red already by that time, but it may be a bit early to tell sex on those.
You asked if there would be anybody there--how would we know? You didn't say where it was, in what state or city.