Gender-neutral 'SIR' equivalent?

In a customer-service environment, how should one address a customer who appears to be or identifies themselves as non-binary?  Is there a moniker that is 'safe' if you don't know?

I don't know of a non-binary equivalent to sir or miss that is spoken.  I've seen Msr or Mx in writing.

Maybe just say "How may I help you?"

"Them"  seems to be the non-binary equivalent to "him' and "her."  Not sure how this would translate into an equivalent for "sir."   

How about, "my friend?" 

How can I help you, my friend? 

My friend, are you going to pay for that?

The_Soulful_Mr_T said:

How about, "my friend?" 

How can I help you, my friend? 

My friend, are you going to pay for that?

Kiwis or Aussies might say ‘mate’, my FIL from the UK originally would’ve said ‘dear’ for either male or female, so ‘friend’ or ‘neighbour’ work just as well depending on setting. 

As a woman who gets called "sir" all the time, I would welcome a gender-neutral courtesy term. It doesn't bother me except for the awkward apology when the person realizes their mistake. 

As joanne pointed out, "dear" works in the UK, but we don't have anything equivalent in the US.

Now that I live in the "ma'am" zone down south, I miss being called "miss" in NJ. Even though it's goofy to say "miss" to someone who's retirement age, I always enjoyed it.

comrade

Shemademedothis says he introduces himself then asks ‘how can I help you today?’. (Handles inbound calls for a Govt service department) 

A timely article (NYT) about another candidate: “sumercé,” or “your mercy.”

DaveSchmidt said:

A timely article (NYT) about another candidate: “sumercé,” or “your mercy.”

Interesting.

Along with the "sumerce" article in today's NYT, there was a question elsewhere in the paper about interchanges where you aren't sure of someone's gender/preferred form of address. The advice was to simply drop the honorific - ie, "Excuse me, please" rather than "Excuse me, sir" or "Excuse me, madam" or whatever.