My best fake buy was a 1937 Australian Crown. I knew it was fake when I picked i up, the seller wanted hundreds of yuan so I promptly explained all the reasons how I knew it was fake using my best body language.
Eventually he offered it to me for 20rmb to get rid off me as there were many people gathering to see what was going on. I bought it and it's now one of my favourite treasures. A real fake Australian Crown from China, that's worth 20 rmb, not many people have even seen a real one.