On Tuesday I walked into a little kiosk to buy some beer and bread rolls. The woman was shocked and surprised to see me enter the door. I don't think that they get so many customers, but still it was a shop.
It was also a bit difficult because she didn't speak any English. I didn't feel like apologizing much.
A similar thing happened to me when I visited Liverpool one time. I was staying in a pub (it had rooms rather than I passed out). After breakfast I went downstairs to the door. The Polish woman who had made breakfast was standing by the door to the street. I just said "excuse me" because she was standing in the door. She turned around with a shocked look on her face and she said "why are you doing this to me?"
I don't think I walk particularly quietly. I am more like an elephant going clump clump as I limp around, but apparently I am quiet enough to sneak up on women working in pubs or shops.