When considering a grand piano I separate these into four categories. Newer but slightly used, used and well maintained, used but need some reconditioning and vintage, and heirloom quality instruments.
In the newer but slightly used category you will find mostly Asian built pianos. I would use a general time frame of under 20 years old. This is true because there are only a handful of American and European manufacturers left. In this category the piano you are looking for is a clean piano that needs no more than a little cleaning, tuning and minimal action work. These are generally bright in tone and have solid actions. As in other industries each brand has its better offerings as well as less desirable models. These pianos are considered disposable as when they get old and worn are usually not worth a restoration. The cost to complete such work would exceed the value of the piano.
Used but well maintained will still be more Asian instruments but will include some good American names like Steinway and Baldwin. While older these pianos can be a good choice depending on the amount of wear and how they have withstood the test of time. They may have had new keytops, the hammers and shanks replaced, action regulation and even had the cabinet refinished. An approximate age range here is 10 to 40 years. Many of these pianos have been well used but not by schools, churches, or piano teachers.
Next to consider should be used but need some work. These pianos can be more challenging but very rewarding. With the approximate age being from about 30 to 90 years old, these pianos have lived well and seen some use. Your find may have been partially or completely rebuilt already. Perhaps it has been rebuilt but not refinished or restrung with a new finish but needs a new action. There are many different scenarios here that require a trained technician to evaluate and assist in weather it is worthwhile to pursue this endeavor. If done correctly and with some patience it can work out to be very rewarding. One of my greatest experiences was found in storage warehouse where the piano was carefully packed away in a “time capsule”. With a good cleaning and some of the action parts replaced it was in fine condition for another 30 years. It had a rare Louis the 15th cabinet in Circassian walnut that with some minor rubbing had a beautiful patina. While not all of this type will be an art case, there are many pianos that were built to withstand 200 years that have many good years left.
In these situations you should be either working with a piano technician or at least know one you can ask for advice and a consultation PRIOR to purchase. [A side note here. The worst calls I receive are when the potential customer phones to report “ I just got my used …… grand piano delivered what do you think?” Now I have to be the bearer of bad news and at times just walk away in dismay.] Be fair to us both and phone first. In all cases it will be a call worth making.
Finally there is the Vintage Heirloom quality Grand. These are the highest quality, best brand and best vintage, well-aged instruments. The best examples would be Steinway and Mason Hamlin. Although there were several other fine pianos built, their completed value often does not warrant the expense of restoration. This type of piano should generally be purchased after it has been completely restored from a reputable store or shop. It always should be restored to the highest quality using only the finest materials by a very experienced rebuilder. The craftsmanship here is the key since a poorly rebuilt piano will not sound good or age well. This is an investment grade instrument that will appreciate when properly restored and maintained.