Would it be okay if I sold a second hand computer to someone who thought they could get it to work but now can't and wants their money back?
How was it broken?
it was broken already when I sold it.
You should always tell someone buying something of yours why it's broken. Otherwise they could get mad at you about the condition.
What's wrong with delivering something broken?
How would you like it if someone sold you a broken item? It is always important to make sure that something works before you attempt to sell it off as something that does, or else no one will ever want to buy anything from you again.