The Bazaar - S6-E5
Visible crew/equipment: After Andy shouts at Goober to get his pickup truck away from the courthouse, it cuts to Andy, Warren, and all the women in the courthouse, and we can see the chalk T-mark on the floor at Warren's feet.
The Bazaar - S6-E5
Continuity mistake: After Goober complains to Andy about Warren it cuts to Warren walking down the street, and when he moves the bucket of corn in front of the grocery store, the window display and the taped signs change/vanish between shots. (00:02:05)
The Bazaar - S6-E5
Continuity mistake: When Andy looks out the courthouse window and sees Goober's pickup truck filled with the ladies auxiliary group, Andy rushes out the front door and there's a wall right behind him where there shouldn't be, and although there's a bulletin board on the wall it still differs from the real one, plus the wall's air vent and wall trim are missing.
Answer: It was a joke. They were supposed to be dumb hillbillies.
Both. According to later interviews with both Andy and the Dillards band (the real name of the band that played the parts of the Darling children, of which Charlene (Maggie Peterson - Mancuso was also a member) the reason the Darling boys never had any lines was because they would've had to have been paid if they spoke. In return for appearing without lines or pay, Andy promised to get as much of their music onto the show as possible which, he did. This obviously gave them a lot of exposure.