If you sold ice cream on the street and needed to figure out how to become profitable, would you be so opposed to trying out selling at $5 one day and $7 the next? Or would this be too unfair to the people that paid $5?

It's the intent I guess. The bartender story seems to imply a bad reason for the discrepancy (some type of unfair discrimination), while in this case it's to find out if you can charge more to eg capture back more of the value people are getting from you. Which doesn't seem so bad.