Pianos age the way houses or people do. When they are 80, 90 or 100 years old they always need a great deal of work, the cost of which will exceed the price of many new or newer entry level pianos: if a piano is going to be enjoyed inexpensively, then a newer instrument is a better candidate.
Most people buying old pianos focus primarily on the sound, forgetting all about the complex mechanical system controlled by the eighty-eight keys. This mechanism wears out and replacement components are expensive. The older the piano, the more probable it is that the machine is worn, resulting in "touch" that is noisy and very inconsistent.
Any piano buying decision is a blend of three components; a good long-term musical instrument, a piece of furniture you like or can accept, and an amount of money you are comfortable with spending. You may give up some of one component to get more of another, but remember a piano is something you must live with for a long time; it is important to be comfortable with it musically, financially, and cosmetically.
Pianos hold their value well, in fact well enough that Robert Lowrey will buy a piano $6000 and under back from you, or take it on trade at 70% of its original purchase price for 3 years after purchase. Long-term dependable pianos may cost a little more, but your money is safer, and the musicians in your home will be more inspired.
Most people pay too much for old pianos; the as-is value of old pianos is actually quite low. Unfortunately however, a naive buyer may see new pianos for $4,000 and think an old piano they see privately for $800, is a bargain. In reality they will probably pay $600 too much, particularly if it requires thousands of dollars worth of work.
Pianos don't age like violins and guitars. The strings in a piano create literally tons of stress which takes its toll on soundboards, bridges, and pin-blocks, aging a piano far more quickly than other strung instruments. Moreover, there is nothing between your fingers and the strings of a violin or guitar, but when you play a piano, you express yourself through a very complicated machine that wears out as it is used.
Many parents think any old piano will do for their children starting out. If these parents knew as much about pianos as they do about bicycles they would realize that their children were about to go on a bike with flat tires, a bent frame and twisted wheels.
If you find a younger piano, bear in mind that even if you have been very lucky and found an instrument in excellent condition, it would cost at least $400-$700 to put it in a similar condition to one you'll find at a reputable dealer showroom floor. Older pianos require expensive repair.
If a piano passes a common sense test (the price is right and it does not seem to have been abused), you might leave a deposit subject to approval by a technician. Bear in mind, however, that many tuners are not really technical people, and may not have a lot of experience with the mechanical system of pianos.
Many advertisements in the paper which appear to be private people selling pianos are really dealers, and they are usually selling dubious pianos with inadequate work performed. Please feel free to visit Robert Lowrey and ask for advice! - The staff will be happy to counsel you on your prospective purchase, with absolutely no obligation.