Might I suggest that a proposal for re-building or restoration of
a mechanical musical instrument list what is covered in the proposal,
for example, key or note pneumatics, bellows or pump work and all other
components that the restorer would know resulting from his previous
experience.

The proposal might also include a list of things that would not be
covered, as in most professional proposals.  I would think that might
go a long way in dispelling any doubts the customer may have regarding
what he (or she) will be paying for.

Cecil Dover