I just got a used a100(~2000 shutter clicks). Sometimes the picture will take as framed. But i have noticed a few times that when i take a picture it is framed lower than what was in the viewfinder....
Is it possible the sensor shift is getting stuck at full deflection?
Had it happen with mine, there is a issue in the Sony cameras that the mirror moves after a while.
I asked around and a guy I know who works in a camera store moved it back by hand, its fine now but I'm waiting for it to happen again.
The newer cameras have been fixed.
There were a few little issues with the sonys, one also being the screen cracks very easily but its covered for 2 years.