Consider the needs of the person(s) playing the piano in your house, but you should also think long term. A good upright piano in average household conditions will last 40-50 years before needing a major overhaul, but many have lasted longer. So you want to buy a piano that is a little better than you think you deserve. Because they live in your house, pianos are like furniture so the look of the cabinetry or case is important to most buyers. This will also affect the instrument's price.
A piano has to fit in the space you have for it, and there are many sizes of pianos. Almost all pianos have 88 keys (the smallest sizes have fewer, a couple of models have a few more). The most important size difference is between the grand piano (in which the soundboard, on which the strings are stretched, is laid flat) and the upright piano. An electric keyboard could be considered as well. The grand also comes in two sizes, “baby” and “concert.” There are qualitative differences in sound and action between a grand and an upright, so serious pianists will eventually have to practice and play on a grand piano, but you probably don't want to begin there, as grands are also much more expensive.
Brand new, full uprights are between 50 and 52 inches tall and are about five feet wide. You need about four to five feet of depth (including the player and piano bench). Uprights sell for anywhere from $3,500 to $10,000 and some uprights sound as good as their more expensive baby grand cousins. There are two smaller, less expensive sizes than the full upright piano; the studio piano (45 to 48.5 inches tall) and the console piano (40 to 43 inches tall). Up until World War II, an even smaller size, the spinet, was popular. A good rule of thumb: the larger the piano, the better the sound.
New vs. Used
The advantage to buying a new piano is that it has been inspected and tuned and has no hidden history. Most people, though, buy used because of the lower cost. The disadvantage is that used pianos can have many hidden problems—pianos have thousands of parts that wear down. You should never buy a piano you haven't tried out (or had a friend try out) especially a used piano. You can avoid the worst pitfalls of buying a used piano by going to a reputable dealer. If you're in the market for a $100 piano, you should expect to do an overhaul that will cost at least another $200, depending on how beaten up the piano is. If you're buying used, look inside it at the major parts: http://www.pianoworld.com/buypiano3.htm
If you buy a used piano that hasn't been retouched, a technician may be able to improve the action of the keys. You can also ask a technician to clean the instrument, which may include replacing some of the felt on the hammers, which wears with use. You want to make sure that there are no cracks in or major warping of the soundboard before you buy the instrument. If a piano has not been tuned in a long time (more than six or seven years), it may be impossible to return to a completely even tuning. That won't matter for most uses, and it depends on how out of tune the piano is. In general, don't buy an antique if you want to really play it.
Even if you are buying a piano for a beginner or a noodler, don't leave the instrument untuned and with broken keys or dead spots. That's a real turnoff and the instrument will soon be left unused.
Three things to pay attention to
- Overall sound and resonance. This is often a matter of taste, but there are all kinds of instruments out there, and it won't hurt to be a little choosy. Take your time.
- Key action: Should be springy with enough resistance to the touch as to allow you to control the volume easily.
- Key action, part two: Grand pianos have faster, easier action than uprights, because gravity helps out the keys and the dampers (which stop the sound, when you release the key) and also because they have a repetition lever, to make repeated notes more reliable. In an upright, you should make sure that you can repeat notes quickly (try playing (C-C-C-C-C as fast as you can.) And if you give the key a light, flat strike, you should hear the sound get stopped almost immediately.
You can and should bargain over the price of a piano (unless you're buying one of those $100 jobs from an estate sale.) It's a lot like buying a car. Comparison shopping is a good idea.