That's because you're an honest person.
Sadly, many on ebay, Etsy, Poshmark, Listia, and other trash sites know exactly what they're peddling and they don't appreciate being called out.
Although I'm not sure how other sites handle it, but be warned that ebay's messaging system isn't intended for the purpose of notifying members that they have a violation in their listing. They will and do naru people for "misuse of the messaging system." They advise that you use the "report" button to report fakes.
I'm not trying to preach but I do know of people who were suspended for doing just that and I'd hate to see it happen to you.