Parts - buy/sell to help fellow members or make $?

I had some parts for sale at a swap meet. A vendor made me an offer, on them. After a little haggling, I sold them, to him. Awhile later a friend came to me and said that "SOB", was selling the parts he got from me, for almost twice the price he paid me. I said "what's the problem", I got the price I was looking for. He owns them, and can do whatever he wants. I could have asked the same price he was asking, and maybe they would sell, and maybe not. As it turned out, the vendor had them at many swap meets for at least a year, before he sold them, and got his "return on investment". I was happy with the money I got, the vendor (business man) got his profit, and hopefully the buyer was satisfied with his purchase.

PS: what my friend thought meant nothing, as he had no horse in the rodeo.

PPS: That vendor has found me some parts I needed, and couldn't find, and sold them at a cheap price (a couple of items free).