Straps and buttons: the one failure that drops an instrument
Why straps come off the button rather than breaking, what width and material change over a long set, and the cheap fixes that work.
Bass strings: gauge, winding and what each change does
Roundwound against flatwound, what a heavier gauge really changes, and why a string change sometimes means a setup.
Wall mounts: what the neck actually rests on
Fixing into studs, why the hanger padding matters more than the bracket, and whether hanging by the headstock is safe.