There are several things to look for when buying a used piano. Check your local paper on Friday morning, as most have a special price for weekend ads. The best deals will usually go quick, so check it early. Also, check the weekly classified paper in your area on the day it comes out to get a jump on the best deals.
After you find that prospective gem, play all the keys to make sure there is a sound. Don't worry if the sound is off, a good tuning can bring it back to life. If you do not hear anything when you play a note, either the hammer is broken or there is no string. You can also open up the top of the piano, and take off the front to make a visual inspection of the hammer and strings. The bottom panel on the front of the piano is also removable to check the mechanisms for the pedals.
When it comes to the pedals, the one on the right (sustain) is the most important. Depress the pedal and run your hand along the keyboard, playing all the notes. Do this from one end to the other. You should hear a thunderous sound, which means the sustain pedal has lifted the felt off of the strings and is working properly. The left pedal will make the sound softer, and is usually used whenever pianissimo (pp) is used. Most beginner and some intermediate students don’t ever use it.
If the piano you are contemplating buying has three pedal, the middle one is least useful ( or most useless!!) Its function depends on the manufacturer. Sometimes it sustains the lower portion of the keyboard, and sometimes it sustains notes you are holding down. On newer models, it works like a muffler. By pressing it down and pushing to the left, it will lock in place and make the piano very soft. It’s sometimes called a practice pedal, meaning you or your child can practice all the time!!
Tempo School of Music