Yes, I do, lol!
I actually contacted a seller once to tell them that their pony was a fakie. They had described it as a genuine MLP so I sent a very polite message correcting them. She emailed back having relisted the item with a more accurate description and sent me a lovely message saying how grateful she was that I pointed it out!
I may have got lucky with her though, and I wouldn't make a habit of it as some may not be so nice about it. I felt good for doing it though