The rims on Merle's car switch from chrome to regular spoked wheels, and then back again.
When Merle and Michonne are driving, Merle's window is down on shots from inside the car, but when he stops the car, the shot from the outside shows that the window is up.
Merle's blade wobbles when he's being beaten, exposing it as rubber.
When Rick watches Michonne walk back after talking to the group about his decision he lifts his rifle then puts it down. As he puts it down blue sky can be seen through the sight which wouldn't be visible if the sight was real.
The car that Merle and Michonne get in to at the motel has looks to be 22'' wheels on it. When Merle get to where he is going with the walkers, just before he jumps out of the car you can plainly see the car has "stock" wheels on it, and when he jumps the car is back to having the custom wheels back on it.