A piano tuner will NOT tune your piano unless you pay them. Piano players can hear when the piano is out-of-tune, and since many of them have perfect pitch, playing un-tuned is excruciatingly painful and not an option.
Piano players will often play a freshly tuned piano (that they paid out of their own pocket to have tuned) with minimal, or no, pay.
A guitar player has NO money to pay for having their instrument tuned. That leaves them with two choices:
(1) tune it themselves
(2) play it un-tuned (very popular and economical solution since they usually can’t tell the difference)
Those are the main differences.
Sincerely,
Guitarist