Doesn’t Understand The ‘Custom’ Part Of Customer, Part 11

(A customer comes into my shop and wants to exchange a dog harness for a bigger size. Not usually a problem. She takes out the item; it’s not one of ours.)

Me: “Ma’am, that doesn’t appear to be something we stock here. Do you have the receipt?”

Customer: “Oh, I didn’t get it here. I got it off of Amazon. Can’t I just exchange it for a bigger size?”

Me: “I’m afraid not, ma’am. We don’t accept stock from other shops. You can’t return it here.”

Customer: “Why not? Surely you can sell it on?”

(I then had to explain that we don’t work on a bartering system. I ended up selling her something else. Bonus: she came back four months later and tried to return two dog harnesses, still not from my shop, for a more expensive dog harness than she’d bought previously.)