Once my husband was in M&S looking for wellies for our son, and the sales clerk said they didn't have his size. So my husband asked if she could check online, so she did (acting like it was the strangest request ever). She looks it up, and the computer says there are some in stock online, but for some reason the woman said they weren't. My husband was like, "Um, I can see RIGHT THERE that it says they are." And the woman was like, "Oh. I guess they do have some." Pause. "So... could you order them?" Pause. "I'm not sure how to do that." Silence. Finally my husband got so frustrated he just left. This wasn't some surly teenager, she was a middle-aged woman. No attitude or anything, just... lots of blank looks.
But like I said, we both have had some excellent customer service experiences here too.