A useful example can be seen in the used market for the Alvarez MD60.
One Reverb listing described an MD60 in excellent condition that had aftermarket EMG electronics installed and included a hard case.
This demonstrates an important valuation principle.
An upgrade does not have a universal monetary value.
For a performing guitarist, installed electronics might make the instrument more useful.
For a buyer seeking originality, the modification could be neutral or even undesirable.
Therefore a professional appraisal should ask:
Was the guitar permanently modified?
Is the original hardware included?
Was the installation professionally completed?
Does the modification affect the top or internal bracing?
This is why photographs and complete information are more useful than simply saying, “My Alvarez is in good condition.”