Let me get this straight, you have admitted that you are price gouging because the market is ripe for it. You have admitted you made a substantial profit from this transaction. You have admitted you made a mathematical mistake because you were too lazy to double check your math until after the transaction was complete.
Now you somehow believe it is the buyers fault for not correcting your error and feeding your greed?
So your buyer drove a considerable distance to purchase your overpriced stuff. Did he agree to the purchase based on the price you quoted him? If so why do you think he should give you additional money just because you made a mistake? Was he willing initially to pay full price for your stuff?
Yes, yes, and yes. Op attempted to royally price gouge another member, his plan was foiled by simple math. Then wants to question one's morals. That pretty much sums it up.