During the scene after Lester Dawson leaves the store to a Accordion convention, Ally tells a man that "No, this isn't the eye doctor". The man turns and knocks over two cymbal stands. After the next shot, it only shows one cymbal stand.
After Trish makes her entrance with her yo-yo's, you can clearly see that the cymbal stand is still standing. They must have shot this scene before they shot the scene where the man clearly knocks over the cymbals.
There are many shots after these where the cymbals keep changing from a standing position to where it lays on the floor.
Ally complains about stepping in kangaroo poop, but when you see where she was standing, there was no poop.
Before Austin performs in the store, Ally, Trish and Dez come out of the door on the second floor. In one shot, it shows Trish running out of the door followed by Dez. But in the following shot, it shows Ally behind Trish followed by Dez.
When Austin asks if he and Dez are the only people who are worried for his career, he said "Me and Dez" when the correct grammar would be "Dez and I".
When they are filming inside the Dry Cleaning store, you can clearly see a camera behind the glowing neon clothes hanger sign on the opposite side of the window; the camera is supported by a bunch of black slim metal rods and is probably used to shoot scenes where Mad Dog enters.
In the scene where Austin is performing "A Billion Hits", you can see in the upper right corner by the window a white colored reflection. It is actually the reflection of the wall. In the picture, you can see the reflection of the camera.