I had one like that once - only once - and Icomplained commented (!) in an email to manager, not specifying which assistant but saying that I had always had superb service up to now, but just this once the checkout woman failed to make eye contact once, was sullen and abrupt and kept looking at her watch as clearly her shift was due to end. I got a polite (standard) reply saying they were vigilant about training etc etc but would follow up. She is still working there, more friendly and helpful so maybe it worked. Wouldn't have wanted to jeopardise her job mind you.