A Friendly Sale

I took four tires to a friend’s garage sale and was asking $30 apiece. I needed to leave for a few minutes, so I asked him to watch them for me.

"Sure," he said, "but if someone offers less, how low are you willing to go?"

"Try for more, but I will accept $15," I said, and left.

When I returned, my tires were gone. "How much did you get for them?" I asked excitedly.

"Fifteen dollars each."

"Who bought them?"

"I did!"