I get the impression that they simply would change their face whenever they know you d need tax refund (meaning you are not locals)
I have been shopping there for years but so far no relationship has been secured and whenever I enquire about bags (maybe to have a look at the display as I have never seen a mini K before), I was given the cold treatment....
But I shall say when it comes to scarf, jewellery, shoes they can be the sweetest SAs ever....
Story: there was one time an SA in Sloane street was showing a tourist different ways to tie a scarf and she was really patient and taking the time when a queue to ask for bags started to get long (no SA in leather area and only her in scarf area, you know how close those two areas are so everyone was waiting for her) the tourist was asking if she s keeping her busy but she was in no rush at all. I was actually waiting for her as well as she helped me kept the Brides de Gala heart twillies and I just wanted to pay and leave...
Whenever some guys approached her asking how long they needed to wait, she d be like "I am still with this lady sorry" I cant help giggling in my heart... so she obviously didn't remember me and when we had eye contacts, she just had a brief smile and turned back to the tourist. It took quite some time till I took the courage to approach her finally and said if I could just pay and go and that was the moment that broke the ice.. she just beamed and "oh yes I was waiting for you to come in", called for an intern to help get the twillies out and I just paid and thanked her... so no more bags in London!!! just drop the idea and enjoy shopping for little things...
but I d say if anyone really wants to try, Selfridges would be your best bet! Go in the morning as SA has advised.. just very personal opinion... ^^