Asalaimu aleikum brother

I would destroy them if I were you. The guy sell the instrument to could become a great artist and luring many muslims astray with his musical skills and thus making young muslims addicted to his music and causing even more trouble and fitnah for the ummah.

Ask yourself this; What if the guy that buys my guitar will become the next Micheal Jackson? Dont worry about money, Allah is the one that provides and he will certainly reward you for your noble sacrifice.

May Allah give you the highest positions in jannah and forgive you your sins my brother