How to judge factory strings:
- Run a finger along the wound strings. Roughness or gritty spots suggest corrosion.
- Look for dark or green discoloration.
- Play some open chords. Dull, short-sustain notes point to old strings.
Reasons to change even if they're fine:
- You want a different gauge for comfort or a different tuning.
- You prefer a different material, like stainless, pure nickel, phosphor bronze or 80/20.
- You want a coated set for longer life.
If you change gauge, especially by more than one step, the guitar may need a small setup adjustment. A new guitar is a good time to get a setup anyway, since shipping and climate changes can shift neck relief.