What does the term Vintage imply?
For me, the term vintage implies that the piano is not a new piano but that it is a piano (as a special grape would be off the grapevine) that has been attended to and cared for over the years and due to its age and history, has perhaps some additional value beyond that which can be shown or represented, through the standard retail pricing scales. Pianos as a consumer item lend themselves to this kind of colorful vintage characterization more that most other consumer items that I can think of except for furniture antiques and cars.
