You've asked for an honest opinion so I will give it.
You sold the work so it's not yours.
As you have taken some (or most) of it back, you owe the other guy a partial refund IMO.
I say partial because he did earn some money from it so got something from it.
So he did a lousy job. If he was cleaning windows by squirting tomato ketchup at them, it's still none of your business.
Go on, do the right thing. Contact him and talk about it and reach an agreement on an amount for partial refund.