White Isnít Always Neutral, and Black Isnít Always Live
We know, this is contradicting best practices, but what your electrician understands is that a homeís electrical system is large, complicated, and may have been worked on by dozens of different people, many of whom may not have been properly trained or following code.
The end result is that when you open up an electrical outlet you may find a bewildering birdís nest of wires, electrical tape and wire nuts. That doesnít mean you canít work on it, but it does mean that you need to be very careful and not make assumptions. Always use a non-contact voltage tester to verify that a line is dead before working on it.