What makes a guitar play “bad”?

We’ve all been here. Get a typically used, older guitar in the mail and we open up the case, only to find that the guitar doesn’t play very well. Can we pinpoint the causes?

For me, it’s action that’s way too high and typically too much relief in the neck.

Crappy rusty bridge condition and knife edges on the bridge.

But my main one is oxidized frets. Dirty, unpolished frets will make any guitar play horrible.