Is that used piano really falling apart on the inside and you don't know it?! Buying a good used acoustic or digital piano can be tricky at the very least, or a big disappointment when you do get it, unless you know what you're doing. After 35 years in the business playing, teaching, and selling pianos of all types and sizes, I can personally tell you that buying a used piano, especially in Arizona, is like buying a used car. Sometimes you come out on top, and sometimes you wind up on the bottom.One of the reasons for that is because defects in pianos can either be intermittent (it only occurs occasionally), or defects can be hidden and hard to detect. Both digital and acoustic pianos are very complex instruments and when you subject them to a dry climate like we have here in Arizona, that can create even more problems.
As an example, when you want to buy a used acoustic piano, do you know the humidity content in the piano (or the lack of it)? Are there any minute cracks in the soundboard or pinblock (the block of wood that the tuning pins are in) that can lead to expensive repairs down the line? Do any of the keys stick from time to time when played or are the dampers worn out or improperly seated and adjusted so each note plays cleanly and properly? Do you know if the piano can stay in tune for a reasonable period of time or will it need constant attention in that area due to the fact the piano has loose tuning pins you may not be aware of?
As for a digital piano, those are electronic and the older the piano is, the more problems the piano will likely have? Certain functions don't work but you may not discover that until you have taken it home. Also, older electronic pianos use old technology and in many cases, are not compatible with today's digital music world. For instance, a digital piano using a 3 1/2" floppy disk drive is obsolete because of that technology. Music and midi files are now saved to USB flash drives and SD cards, and for good reason! Some of the keyboard actions used in older digital pianos would wear out quickly or didn't perform properly because our improved technology and construction was not available in those days. But these things may be hard for you to determine if you don't know what you are doing.
And just because the piano may be a popular brand name such as Yamaha, Roland, Kawai, Steinway, Korg, Gem, Technics, Casio, Kurzweil, Suzuki, Samick, Young Chang, or other popular piano names, that doesn't mean they don't have known problems in some of their models over the years.
It can be VERY expensive to repair a piano depending on if you can still get parts for it or if it will need constant service due to cracks or flaws that you couldn't originally detect. Just because the piano has been sitiing in someone's home for a while without much use doesn't mean that it will work right or sound good over time.
So the bottom line is, BE CAREFUL! Extra dry weather, extra humid climates, unknown factory defects that are no longer covered because the used piano has no warranty are all reasons a used piano can come back to bite you in the end. That doesn't mean however there aren't good used pianos being sold, it just means "buyer beware." And just because a person buys a NEW piano doesn't mean there won't be problems because some new pianos are just designed and built bad in the first place.