I go to the library a lot. One of the librarians greeted me, one day, saying "Hello, Sonia".
My name is not Sonia. It doesn't even sound anything like it, but I didn't correct her that first time.
Every time I went in there from then on, I just pretended to be called Sonia. Then one day I had a problem with my library card, she looked down at the name on my card, and I had to admit I wasn't actually called Sonia at all.
Another one, a caretaker at work thought I was called Simone (again, I just went along with it, my name sounds nothing like Simone). I eventually had to own up when his wife started working there, and wondered why her husband was calling me by some random name!
Lastly, I used to do the collections, at work, when people were leaving.
Once I got a bloke some chocolate, iced with a personal message, from Thorntons. It had something like, "We'll miss you, Gordon" iced across it....As he was leaving he admitted that he was known by his middle name usually by everyone outside of work. It was just that he was too shy to say anything as he was being introduced on the first day, so had just gone along with it....I think name ones are quite common.