Principle, Not Pettiness

Found a copy of Misbehaving at Barnes and Noble. The copy was beat up so I thought I could get a discount at the register. Confident that I would walk away if I did not get a price I liked (around $13), I walked up to the register. I got the discount, however, the ending price was $0.50 higher than what I would have paid on Amazon, $14.21, due to the high Barnes and Noble starting price, $17. I asked the cashier if they could match Amazon’s price. They responded by matching to their online price, the original discount. Not wanting to look petty over $0.50, I bought the book. 

I bought a beat up book for $14.70 instead of walking away and buying a new book for $14.21. I am very irritated. It’s the principle.