CVS experience.. afterthoughts

I used software to edit a photo, saved it in USB and brough to local CVS to print. 4x6 photo is 25cents. I selected the photo from my USB and submitted the order, printed out an order slip says .25. Waited for 10 minutes or so, the photo was printed. The staff picked up the photo, she was about to put it into a regular photo envelop, then she saw my photo and changed to an envelop for passport and charged me 7.99.

Me: I printed 4x6 photo, and this order slip says 0.25. Why do you charge me 7.99?
Stupid: You printed a passport photo.
Me: I printed 4x6 photo. I didn't select passport photo or use your machine for passport photo.
Stupid: Those are passport photo.
Me: What I used the photo for is not your business.
Stupid: They are passport photo, you have to pay 7.99
Me: It is photo from my own USB, it is 4x6 photo.
Stupid: You can't print 4x6 passport photo.
Me: I would only pay the price for my order, and this slip says my order is 0.25. What's in my photo and what I use it for is not your business.
Stupid went into the office for a minute or so and came out: You have to pay 7.99.

This is one of the most stupid things I ever come across... Okay, I walked out... Called the store manager, complained to her, she asked me if I still have for the order slip. I said yes, then she said I could come back and will honor the order in the price the slip says. She apologized to me and said she would talk to her staff. She called the stupid staff in the office and let another staff do the print for me. He was a lot nicer and gave me the photo for free even though the manager asked him just to charge 0.25. It took about 5 minutes to print the photo again, when it was done, I saw the stupid staff walked out of the store and got into her car and left. Oh???

Afterthoughts:
1. Did stupid talk to the manager when she went into the office?
2. Did the manager protect her staff or punish the staff?

3. I was grumpy at work today, would I have done differently if I had good mood?
4. Should I handle this differently in an elegant way? -- biggest rule of thumb I have is that as a consumer, I hold ultimate power, and that is the ability to show elsewhere