When Jess and her Dad go into town to get sunflower seeds for planting, they pull in to the feed store and there is mud "sprayed" evenly on the sides of the vehicle, toward the bottom third. Mud usually patterns around the wheel wells and totally up the back side of the vehicle in this rural environment, not evenly distributed. When they arrive back at the house the vehicle has no mud splatters on it.
When Ben is sitting at his table eating, the mom is washing dishes. In the first shot of her washing the plate the water is dark brown like coffee. Ben gets up and walks off and when it goes back to her washing dishes the water is clear.
The ambulance that takes Jess to the hospital has "Balcarres EMS Prairie Ambulance" on the side of it. Balcarres is in Saskatchewan, Canada, the filming location, about 150 miles away from North Dakota, where the story is set.
Sunflowers are harvested after they have gone dry and hang heads down, like mentioned. However, they are harvested with regular combines that are used to harvest wheat, rye, or corn, and not a windrower that is used for putting up hay.
John sees the real-estate agent standing above him in a flashback. It was mentioned that John's family went missing several years ago, but in the beginning scenes of the movie, the real-estate agent hasn't aged at all. He looks the exact same.
The people in the small town, where news travels fast, believe that the Rollins "just up and left", however surely they would have noticed that John Rollins was still in town? Despite going under the name John Burwell and growing a ponytail, he is still clearly the same person; as we see when Jess recognizes him from a photo.