Check for signs of repair where both parts a joined. The tuners shouldn't be lose and shouldn't slip. A used guitar will probably have scratches, but that shouldn't be too much of a problem as long as they don't influendce the playability or the sound. Check if you like the sound. Cheap guitars will not sound like top notch guitars.
More money buys better pickups.
Inspect the headstock. A headstock that has broken from the neck and glued back on the guitar is a bad thing. I wouldn't buy a repaired guitar. The tunesr should be Check the input jack and the controls . Slightly jiggle the cable, that shouldn't cause any scratching sound.