Wire/stud detectors are the only way to be certain. As far as I know the assumption you are making is somewhat correct. Wires go to sockets in straight lines from bottom/top but there are exceptions. What you can do is knock on the wall in a straight line from your socket in order to identify possible junction boxes. They are easily identifiable as they make a different sound.
Asphyxir t1_j59m9e1 wrote
Reply to Installing TV bracket in concrete wall. How to avoid electric wires? by BJJnoob1990
Wire/stud detectors are the only way to be certain. As far as I know the assumption you are making is somewhat correct. Wires go to sockets in straight lines from bottom/top but there are exceptions. What you can do is knock on the wall in a straight line from your socket in order to identify possible junction boxes. They are easily identifiable as they make a different sound.