The cashiers at K-Mart are not trained nor are they required by company policy to check the identification and credentials of each customer that buys ammunition. This is because since they have stories worldwide and the laws for selling ammunition is different for country and the laws can change on an annual basis.
During the sequence about potential causes of violence, Moore mentions that most violent video games are made in Japan. It shows a clip from the Mortal Kombat series. This series, while containing some Asian themes, is actually the product of Chicago-based Midway games.
As Charlton Heston walks away from Michael Moore in the final interview, the scene cuts repeatedly between Heston (point of view from behind Moore) and Moore (point of view from the stairs directly in front of Moore) holding a photo of the slain Flint, Michigan girl and asking Heston to look at it. When the POV is of Moore holding the photo, there is clearly no cameraman anywhere behind him. The same with the POV of Heston, there is clearly no cameraman anywhere in front of Moore. So the two POVs were not filmed simultaneously as the film implies.