Policies have their purposes, but one of them should not be to make customers angry. Properly used, they are guidelines that help an agent navigate the many situations they'll face on a daily basis. If you stick to them without thinking, however, you will inevitably lose a customer.
I visited a Jamba Juice a while back and wanted to order one of their green drinks with kale. The employee kindly informed me that they ran out. I asked if they could substitute spinach.
"Sure, but what will be an extra dollar."
"That kinda sucks, it's not my fault you ran out of kale."
"Yeah, but that's our policy."
If I wanted to add fresh produce to my order, sure, I get that, but I wanted something for which you are missing a key ingredient. Why not inform me of the policy, but provide the substitute at no additional charge? I can either buy an expensive smoothie for which you will still make a profit or leave without a drink.
Seeing the discomfort on my face, she asked her managed who only mindlessly repeated the phrase, "it's our policy."
I left. No sale and this story.