Seller Attempting to Pass off Fake "Vintage" Poster as Authentic. Best Way to Report It?

[mhartzoldbooks]

 I recently purchased what was supposed to be a vintage letter press poster from the 1930's here on eBay (item #172699748902). When it arrived, it was wholly not as described. The dimensions of the poster were way off (the seller advertised it as being 24 x 20 , it was actually 12 x 17), but worse than that, it was an ink jet reproduction on modern paper. It looks like the seller (or someone else, but presumably the seller) even tried aging the paper by subjecting it to moisture and creasing it, but it was still an incredibly bad "fake."

I too am a seller in the eBay marketplace and was drawn to this particular listing because I'd recently acquired an actually authentic example of this same poster (which I sold here as well, item #162559797657). I know my poster was authentic because I am a professional and even had it evaluated by a local expert, a retired printer who worked in a letter press shop for 40+ years who had no reservations whatsoever about its authenticity.

Normally, I'd be inclined to give someone the benefit of the doubt in a situation like this, but the seller already has spectacularly poor feedback and has been largely unresponsive, dragging his feet in the refund / return process. And, he went as far as to write this in his description: "This is the original Yellow Poster not the white copies that have been out."

The "white copies" were my poster and a handful of others that have appeared at respected auction houses over the past 10 years or so. So, not only is this guy selling fake posters and trying to withhold a refund, he's actively dispariging authentic material. I strongly feel like this matter should be brought to the attention of someone at eBay but am having trouble finding an appropriate contact form. When I click on what I think are the correct links in "help" sections, it only gives me the option to call. Should I call? Does anyone know of a good place to send a message about this? Thanks for any help!