Every marked speed timed against a reference, with a result sheet you keep.
A shutter tester reads the actual open time at each marked speed and compares it against the nominal value. Mechanical shutters drift with age, and they drift unevenly — 1/1000 is usually the first to go, then the slow speeds stick.
We test the full range, both curtains where applicable, and check for capping across the frame.
If the numbers come back outside tolerance we will tell you what a service costs before we touch anything. Some cameras are worth it and some are not, and we will say which.