Print a copy of this and take it with you.
*Take the front off the piano. Make sure all keys play. Are parts missing, broken, or unglued? All 88 notes have the same parts so you can compare the good ones with the bad.
*Look at all the movable parts. Are they neat and even, consistent and aligned?
*Are the keys level? If the white keys........when you get down and look at them from their level, look like a roller coaster....it is quite likely the felt is damaged or gone underneath them.......Or the keys are warped.
*Check to see if the bridle straps (small cloth strap from one part to another) are in good condition.
*Are any keys sticking or sluggish? Two or three are not a big concern, but a lot - costs a lot.
*Are the keys evenly spaced, square with each other?
*Are keytops ivory or plastic. Are any missing, chipped or damaged?
*Move the keys to the left and right quickly....not up and down. They should barely wiggle and should not rattle or click.
*Move the hammer gently left and right (not forward and back) to check tightness. If they wobble, they may hit the wrong strings. Clicking sounds when played indicates loose screws or possible loose glue joints.
*Play all notes staccato (except where there are no dampers) to see if the sound stops quickly. If not, the dampers may need to be adjusted or replaced.
*Do all the dampers move together when the right pedal is depressed on both the grand and upright? If not, alignment needs to be done.
If after checking these things out, you still like the piano, contact me, [the "Piano Guy"] and ask questions. Many of the above areas can be “repaired” with reasonable expense.