Good before and after photographs are taken from exactly the same position, at the same height, in the same light. That is the entire technique, and it is the step nearly everybody skips.

Most before shots are taken in a hurry from wherever the person happened to be standing. The after is then taken from somewhere else, and the pair proves nothing, because the viewer cannot tell how much of the difference is the work and how much is the angle.

Mark the spot before you start. Same distance, same height, same time of day if you can manage it. When only the work has changed between two frames, the photograph makes an argument that no sentence on your website can.