I agree that "they" for singular when you do not genuinely know has always been around, and not new. Though grammatically incorrect, I've used it in that sense and probably will in this post. What I will not do is refer to someone as she, when that person is clearly male, and vice versa. I don't placate feelings. I will be loving and friendly and would give the shirt off my back to anybody, but I do not violate my beliefs.
On shops, I will not use "they," if I am talking about one person. I will use "The associate" or "the employee."
There is a clerk at one of the post offices I shop who I'm unsure whether the person is male or female. The name does not help. He or she does not appear to do anything deliberately to be one or the other, nor does it appear they do anything deliberately to not appear one or the other. What I do know is that person works hard, smiles, helps customers, and seems to really enjoy the job. As a customer, I can't ask for more.
@ prince - I'm sure the natural food grocery store was a blast. I used to live near one, and honestly it was the neatest place. I could find a lot of stuff that I couldn't find anywhere else. There were all kinds of people who worked there...it was what it was...everybody was always very nice. I actually wish I had a place like that near me now.
There is the truth.
Then there is the right thing to say.