Customer thought I was ripping him off only to return later in defeat

A customer got really angry at me as I was not able to price-match the Diprosone OV ointment 30g he wanted. We sell it for $31.50 and he says he usually gets it for $25 at the chemist down the road.

I checked our cost-price, which was way above the $25 so I just couldn't match it. I told him we are the cheapest in the area and if we can't sell it for that price, don't know how other chemists can. I said the prices have gone up over the years.

Then he continues on and curses me for overcharging him and that he won't ever come here again coz we are ripping him off etc etc....

Well guess what. The same man came back today and I dispensed the script for him.

I cheekily said: Oh you know its not $25 right? We sell it for $31.50.
Him: Yeh what can I do? I need it so I'm gonna have to buy it.
Me: Oh you said you could get it at the other chemist for $25, you didn't end up getting it? Why's that?
Him: (getting frustrated) coz the prices have gone up and they can't do it for $25 anymore.......
Me: Is that so? Yeh I wasn't lying when I told you we're the cheapest in the area. Now you know.