It's called a free market economy. He is free to buy and sell for a profit if he wishes. There is absolutely nothing wrong with that and it is no reason for you to judge his integrity. You sold him a pair of knives for your asking price, the transaction went smoothly and that's where it ends. Beyond that is none of your business, much less your right to judge his integrity.
People like you make me sick, and you have now been put on my ignore list. I refuse to buy from over-sensitive, entitled, whiny little brats like you.