Totally agree with the last paragraph. Also, when you're face to face, eye contact and a nice smile makes for a much better shopping experience.
Recently I was served by a young girl and throughout the whole process she didn't look at me once. I was quite put out by this and said to her as I took my receipt, "Eye contact would have been nice". She looked shocked and I'm sure felt embarrassed too.
I suppose some might think that a bit harsh but I think it's so important in a customer facing role to make eye contact.
Generally, I would pull someone up for poor customer service but it’s on a case by case basis. Two sales assistants talking all the way through serving me will get a reminder I’m in front of them. But as well as asking yourself what they’ve done, it’s more important to ask yourself why they’ve done it.
A sales assistant not making eye contact is odd, and the why is very important in this case. Is it her first week on the job? Is it the first time she’s been left on the till on her own? Did her gran die yesterday, or her boyfriend dump her last night? Not making eye contact suggests there might be a bigger issue than poor service. I’d just thank them and move on with a smile.