I've been to several but never read the fine print on the sign.

I always handle any transactions in the parking lot, in my vehicle or the other person's vehicle. They can't say a damn thing about that. Do what makes you happy. I have brought ammo into shows, to sell/trade more than anything; I have never had any issue at any show I've went to. Now... If its loaded in a magazine/firearm they get VERY sh*tty about that.