There are several considerations in purchasing a piano. Are you looking for the look and sound quality of a grand piano or the space consideration and affordability of a vertical upright? [Console or upright?]
Here are some basic guides that apply to both. Piano strings are generally good for about 50 years. Past that and the wire begins to fatigue and breakage may occur. Also the tuning pins may become loose rendering the piano unable to be tuned. While these problems can be corrected, as a technician, I would rather see the average consumer by a piano that is ready to enjoy, not a fixer upper.
First we need to understand a little history of the piano. While the piano was invented in 1709 by Cristofori, the modern grand became of age in the late 1890’s. This is relevant when we talk about a vintage grand for restoration but has no value to the vertical buyer. The largest number of quality pianos was made in the United States in the 1920’s. There were thousands of manufacturers during that time, many of very good quality. Unfortunately most manufacturers did not survive the depression.
When we talk about verticals the story is a little different. While the first big old uprights were made in the teens few have survived and a fewer are worth investing in, they are too old to justify the expense of restoration. In today’s market I generally do not consider pianos prior to 1970, since most verticals do not justify restringing.
Once you have decided on grand or upright let’s consider a few obvious factors. The brand name and serial number is a good place to start. This helps determine quality and age. If the instrument has fire, flood, water or smoke damage or has been dropped, pass. Why start with possible damaged goods? Has it been moved around a lot with marred cabinet or missing parts? If so it is not a strong candidate. Keeping in mind that many of these conditions can be remedied if you ALREADY OWN the instrument, why would want to speculate when cleaner prospects exist? A piano that is a one owner or stayed with the original family is a plus. A last tip is not to acquire a piano from a school, church, piano teacher or charity. These pianos are almost always poor choices for when these people are finished with the instrument usually the instrument is finished as well.