The customer who asks Glenn for bleach turns around twice.
When Glenn is speaking to the male customer with the murder implements in his cart, the items in the cart move between shots.
After Glenn gives permission for Jonah to clock out and leave with his parents, Jonah goes to the break room and retrieves his coat from his locker. His parents had seen him around the store without a coat on. Emerging from the back of the store suddenly wearing a coat should have raised suspicions about where the coat would have come from.
Jonah is forced to reveal to his parents that he works at Cloud 9 and therefore is not attending medical school like they thought. Medical school is expensive and his parents are clearly not supporting him financially. He could have easily told his parents that he was working at Cloud 9 to put himself through medical school, rather than as an alternative to being in medical school.
When Glenn is speaking to the male customer with the murder implements in his cart, Glenn somehow fails to take notice of a machete right at the top.