Sorry this happened to you.  Can you reply to the review and calmly and factually show it as false?  On yelp and other sites this is possible.  Beyond that, keep trying Zillow and try to find contact info for people higher up in the food chain and contact them directly.  Hopefully you'll get someone willing to help.

Oh, and FYI if you respond to anyone's questions those responses won't be anonymous.

1. Soap Box: Zillow reviews are owned by Zillow. I never ask for reviews to be placed there, they control them. I did in the past have clients that went there to do so, but I guide them now to my Google Business page. Equally not owned by me, but way more in my control with customer service that seems to care so far. 

I think Bob Crane gave a great answer, in fact similar to my first thoughts so I'll try to offer others here...

2. Answering your question: I'd reply professionally, stating either addressing "this person was never a client of mine" or if they were, I'd share that "I'm sorry you felt that way, you can see from all my other reviews it's never my goal to do anything but wow my clients. May I a remind you though that 1. fact 2. fact 3. fact." Remain calm, professional and polite and deliver the facts. A ad review is to be expected occasionally, typically they are an unreasonable person leaving them. I see bad reviews for my favorite restaurants and hotels, they are usually so specific to that person that I couldn't see me ever having the issue they claim. Common Sense People see through the b.s. 😄

You've received some good suggestions on how to handle this. I doubt any attorney would take a case like this and if one did, I can't imagine what it would cost you... probably a lot. 

If you know the person I'd contact them directly. If you don't know, and it's totally bogus, there is a "report a problem" button. If that doesn't work, perhaps there is a Z facebook page or linkedin page that might have information on how to proceed. Or that you could post a request for help on.

No response is best, see if Zillow can help but don’t sweat the small stuff.

Honestly,  I am not sure how helpful reviews might be.  Anybody can draft and post them on most sites.  It is always interesting to see some of these reviews posted by disgruntled folks.  Take it for what it is worth.  

No clue really. Don't use Zillow and don't hold myself out as a techie. Good luck!

1. I would have never noticed any reviews on zillow.

2. Is it worth your time to worry about what z has to say about you?

3. If it does bother you then bury it with a ton of good reviews on z, get your friends and relatives busy writing.

I had this happen to me on Yelp.  Wasn't even a past client.  Turns out it was the husband of a Realtor who lives in my neighborhood.  I contacted Yelp, who did nothing, but suggested I join and then they would remove it.   So I wrote a scathing review about Yelp.  That was removed within 24 hours, although mine was 100% truthful.  Just post enough good stuff to cancel the bad-- and have a good answer if a future client asks you about it.  Maybe explain why it is a shining example of how inaccurate Z can be on everything, and not to be trusted.  

Choose your battles! Some are not worthy of your attention. Consider also that others can see clearly when there is one-sided bias bashing and dismiss accordingly. Relax. Not wise to battle in public. It becomes entertainment

I’ve handled 3 cases of online disparagement.  Here’s a brief description. 

1.   This case involved a defamatory statement.   An attorney letter did the trick because defamation per se carries a claim for punitive damages, which is a scary prospect.   The Author removed the review  

2.   This case was not defamatory and was borne from a dispute.  I contacted the author directly and negotiated a settlement which called for removing the review.  No attorney letter and the tenor of the conversations was kind and respectful, whereas the client’s attempt was hostile and menacing.  (The author ofthe review became a client of mine in an unrelated matter)

3.  This case involved a customer who genuinely believed they had a bad experience and used no defamatory language.   No attorney letter, just two telephone conversations.   Unfortunately, I was unable to persuade client’s customer to rescind their review.  

Of the comments here, I most endorse Lynnea Miller’s.    Deal directly with the former client in a cordial and respectful manner.  The moment you get belligerent and self-righteous is the moment you can expect a poor result.    

Generally, Ive found a client’s biggest challenge is self-honesty.   If there’s any merit whatsoever to the bad review, acknowledging it in a telephone conversation, while asking what they liked about the service is a good way to achieve a balanced and professional conversation. It opens the possibility to the author voluntarily removing the review because you handled the complaint respectfully. 

If the author is unwilling to remove the review despite best efforts, then I would write a professional reply response similar to what Karen Climer suggested. 

Under no circumstances would I let a bad review go unanswered.  if the review site allows for a response.  I believe a lack of response could be viewed as an acceptance of the bad review or statement of not caring.

False as in 'I don't even know you'
or false as in 'I accused you of something you did not do or was not true'

If the former, I'd respond, 'Kind sir, you may have me confused with another agent as I do not know you' 
If the latter, I might keep bugging Z to fix this. I would not bother with attorney, I might ask good clients to add nice reviews to 'overpower' the a-hole . . . 
This is why I do not allow outside reviews except what I add to my website. Trolls abound. Stay focused on the next great job for a good client.

My tendencies would be to just ignore it, Z is a "has-been" and never was much of a factor in my area. If I were to respond it would be without emotion and just a factual rebuttal. Getting down in the dirt just gets you dirty.

I have responded because Z won't help at all unless they are not your client. It's hard to respond & not get angry but that's what you have to do & then just let your view hang out there. Your version.

I do not have experience with Zillow reviews specifically, but I have experience with other platforms.

First, read the review rules for Zillow and see if they violated any rules.  For example, some platforms say you can't use anyone's name, so if the review said, "Bob was a terrible server," the restaurant can get the review removed (even if it's true).  So check the rules and see if there are any rules like that they the reviewer violated.

Second, post a factual response and the target market of that response is not the person who left the review, but your future customers.  If there are any allegations that are true, you can acknowledge them.  For example, "You are correct that it took me 72 hours to return your call.  I was in the hospital with COVID.  Typically, I return calls within 24 hours.  I apologize for not handling your call as promptly as I normally do."  If there are inaccuracy, you can address them.  An inaccuracy is a fact, not an opinion.  If the "inaccuracy" is an opinion, just ignore it or address the audience.  For example, "Bob was rude to me."   I would ignore and say, "I'm glad we were able to help get you into your forever home.  I wish you and your family the best."

If it's a fact, address it. "She didn't advise us to get a home warranty."  You can address that by saying, "On January 3, you signed an acknowledgement that I offered the warranty and you denied coverage."

Mostly, you need to respond with something.  Respond in a way that you would treat your future clients.  Focus on facts.

I don't believe anything will be done by Z.

Good luck.

There are great responses here. I had a person remove a bad google review by responding to him and asking him to call me - which he did.  It appears that his review was based on rumor and innuendo.  When I spoke directly with him, he found out the truth and withdrew the poor review.  

Lots of very good and interesting suggestion on this thread.

Hiring an attorney would be a complete waste of time and money.

Responding can be a double-edged sword.  Most of the time, the public can discern, when they see 15 great reviews, and one clinker, that it's an aberration, and not the norm.  Sometimes it's best to just leave it alone. 

To be honest, I'm not sure how I would handle it. Depends on what it said. People are entitled to their opinion. It's like getting zapped on YELP. You can respond but do it professinally

Yikes! I can't imagine an attorney would be the cheapest route. I would probably respond back with factual information so that the public can see your response. Perhaps the author will be alerted of the response and realize they left it on the wrong agent's profile? 

Good luck!

I've had one bad review but it was on Google, who did nothing.  I did however respond to it in a very professional manner that I had looked through call records and had no record of that number calling my office and left my cell number. (it simply stated we did not return a call to them)

If 95% of your reviews are great, I think it is obvious to the "reader" that it's sour grapes, or even fake.  I say "ignore" unless it's harmful accusations.

An attorney where?  Because unless you know the person who did it and it's false and you sue them where they live....  just respond professionally, ask for some other reviews and drown it out.