What would you do...?

I emailed a company to find out if one of their second-rate products I saw on eBay was genuine as the price was too good to be true (I didn't include a link, just photos). The company indirectly admitted to its authenticity but said any they have are donated to charitable organisations and that any on eBay are stolen and are illegally being sold. The company then said I should feel free to let them know the name of the seller if I wished. Prior to contacting the company, I emailed the eBay seller to find out more about the ad, return policy etc. and he was very helpful. I would feel quite awful if I reported him but at the same time it isn't right if the items are illegally being sold, but then does the seller even know they've been stolen? It is worth noting that the company originates from the US and the eBay seller is based in the UK. What would you do?