debunking  

This happens to me too. Most ...
This happens to me too. Most people don't care as long as there is a good name attached to their third rate, non designer slop.

Mileage Varies
I have found that having absolutely impeccable research to back up my claims helps a little bit in debunking.
Most folks when presented with absolutely ironclad evidence will change their listings accordingly. Especially if the evidence is published and widely disseminated so as to make it difficult to ignore.
But still there are the occasional hard asses who would rather be wrong than admit to having made a mistake and also of course those persons who are just outright deceitful and knew all along that their attributions were incorrect...

In the early days of Ebay, I...
In the early days of Ebay, I was amazed at the number of knockoff Eames lounge chairs that were listed with "authentic","Herman Miler" or "genuine." Sometimes the seller would add a question mark, which made me wonder if they were really uncertain, or just wanted to avoid culpability for their inaccurate claims. My favorite misinformed listing referred to Charles and Ray as the "Eames brothers."
So for a couple months, I took it upon myself to email each of them, pointing out the differences between their chairs and the real thing, often sending marked up photographs to illustrate the discrepancies, and answering multiple follow-up questions. About half the time, the seller would thank me, and change the description to reflect the new information. About half ignored me.
There was, however, one seller who sent me back an email full of expletives, telling me it was none of my business. In turn, I emailed the information to all the bidders, whose business it really was.

I contacted Sotheby's recently about a Mario Sabot piece masquerading as Willy Rizzo, they thanked me and did nothing whatsoever....because it suits them to use the Rizzo name.