One day, our local grocery store overcharged me for a product that I did not buy. (I think the casher scanned twice by mistake.) I wanted the money back but I had come home already and wasn't sure how I could prove that I didn't have the product. But the similar things happened several times before and this time my loss was more than $10 - I was ready to fight with the store. (`・ω・´)
I went back to the store and started explaining to a casher. Before I finished explaining the whole story, he gave me cash back and said "Sorry about that."
After living in America for ten years, I'm still amazed how easy to get a refund or exchange here.