All of the above! I like to think that the customer deserves a little respect . Shop staff are called assistants, and that is what they are paid to do...assist. I am unfailingly polite to staff in shops, cafés, bars etc.....but I do NOT want to be treated like their new best friend. "may I help you?" Or "can I be of assistance?" helps to make a shopping expedition a little more special..particularly when the word Madam is added!
I do NOT want to hear "you all right there?" Or "You ok?" from a bored individual who has forgotten how to make eye contact due to overuse of a phone screen.
The terms 'love, darling, sweetie, dear etc ' - including colloquialisms such as 'duck, chuck,m'dooks' etc are sweet, but still too familiar.
Mr Selfridge...whereart thou? ;)