I genuinely do understand customer service and trying to be polite and helpful to everyone, but I think it doesn't dawn on many staff members that some people use self-serve because they cant use the tills and interact.
For example, if your item doesn't scan right and needs intervention or there's age restrictions it's totally understandable for staff to pop up and sort that for you, they're always quick off the mark and very helpful.
But, if there's tills available and I'm waiting for self-serve I'll often be told to go to a till, surely it's my choice whether or not to use the open till? I'd say it was being helpful except I have eyes, i can see the empty till 
I then have to say "no" which shocks them every time and being stereotypically British as well as not NT that's horrid for me to do.
It's that same if they come over to chat or comment about what's in your basket, I understand while serving on a till but are they told to do that with self-serve as well? My biggest issue is someone standing behind me and watching me scan everything like im either incapable or trying to steal. Also not giving me more than 0.5 seconds to let the machine adjust to the new weight in the bag before popping up behind you. Although I'm likely bias with that as someone physically moved me out of the way (yep by touching me, big nono) and the machine was back on track before they even reached it 