I can repair and tune all kinds of accordions to a high standard. I can undertake complete restorations of vintage piano accordions if the instrument quality merits it. Nearly all the instruments I have restored, repaired and tuned can be seen and heard on my youtube channel 'Accordions South West'
Tuning an accordion involves measuring accurately the pitch of each and every reed both push and pull. To tune the reeds the reed blocks need to be removed from the instrument, and that changes the pitch of the reeds in a somewhat unpredictable manner, so careful adjustments need to be made by filing the reeds the correct amount up or down. Fortunately tuning does not have to be very often, but unfortunately most accordions I see have never been tuned for decades
The reed valves need to be in good condition to tune accurately. Leather valves dry and curl after 40 years or so and usually need replacing which is a major job.
The pallets on the end of the keys are leather and felt and can harden, some pallets like the Lucia pictured had foam instead of felt which perishes after 20 years or so and must be replaced necessitating adjustment of keys using specialised bending tools