Guitars and basses: check the neck, frets and action

Sight along the neck and look for obvious warping, twisting or irregularities. Then play through the entire fingerboard using normal dynamics.

Check:

• fret wear and flattening;
• notes that buzz or choke prematurely;
• unusually high or low action;
• tuning stability;
• any cracks around the headstock or neck area;
• available adjustment range where the seller can document it without invasive work.

A poorly set-up guitar may simply need adjustment, while heavily worn frets or structural issues can require more substantial work.

Do not judge only by the first impression. Try to separate setup, normal wear and actual defects.