A small Nebraska town will have almost zero swimming pools outside of a public pool or two. A private pool service would be a tough way to make a living (which is probably why he didn't have any clients).
In the pizza shop after John is jogging he is talking to Nedderman his
shirt is covered in sweat, but in the next shot it is not, and then in the next shot the sweat is back, then the sweat is bigger and then it gets smaller.
When John Farley is about to be interviewed by Tyra, they cover up his face wounds with makeup. Then he talks to his mom, in the same room, and they are uncovered. He goes back to sit down and one is covered with makeup again. Then he leaves, and they're both uncovered.
When Farley and Mr. Woodcock are in the barber shop, the
barber uses the clippers to make a huge, very noticeable bald spot in the back of Farley's hair. When he's getting out of the van at Mr. Woodcock's ex-wife's house, there's no bald spot. Then as he's walking to the door, the bald spot is back.
In the pizza restaurant, in one scene John hits the bowl of food and it's all over the counter, in the next scene, all the food has been cleaned up and is neatly back in the bowl. Not enough time had elapsed for the contents to have been cleaned then placed back into the bowl.
In the bar scene with John and his Agent, she checks her Treo for a message about the Corn Cob Key and then puts it down on the bar. The next shot John has it and he puts it down too. During the rest of the scene, using the same two or three angles, the phone's position changes back and forth.
After Farley finds out about his mother's engagement, he storms into the Toby's pizza restaurant and while "venting" he grabs a slice of pizza, disturbing the entire pizza. However, the next time you see the pizza, it is back in its original undisturbed position.
When Farley and Nedderman are about to break into Mr. Woodcock's house to plant the video camera, we see several shots of them moving through the yard and into the house, and neither one is carrying the camera.