When the tractor breaks thru the doors Bagley is seen in a shooting position with his rifle. He shouldn't be. Just moments before he was content with the boys going up in flames, therefore he wouldn't be leaning out the window moments later aiming a rifle at the barn.
When starsky and hutch are in their car you can see that its a moving screen behind them meaning the car is obviously in a studio and a screen behind them they used to do this back in the olden days westerns in particular ie stage coaches etc.
Hutch couldn't possibly describe what the girl stole (a lighter) because he wasn't looking when the robbery took place: he was trying to get Starsky's attention. The same, she stole behind their backs and when Starsky flew after her, it didn't make sense, as he was acting as if he'd seen her steal something but clearly she was behind him when she took the item from the shop.
When Starsky and Hutch are tailing the tan van, it hardly seems worthwhile that they slink down in their seats, so the crooks can't see them, when they are in a bright red Torino with a big white stripe down the side. Especially when the crooks spot the Torino seconds later.