Many years ago I won a denarius from a member auction on a well known site. I had never bought from this particular member before. When I collected the Registered Mail envelope from the post office, I noticed the postage stamps indicated it came from Bulgaria. I was a really green collector, but I knew to avoid coins from Bulgaria. My heart sank.
When I tore open the envelope I saw there wasn't any self-adhesive coin mailer inside, just a coin wrapped thickly in some newspaper. I thought that was another bad sign.
After removing the paper I looked at the coin and thought the surfaces looked very strange. The colour of the metal wasn't that of clean silver, nor toned silver. It looked like tin or something, although the details were correct but soft. I had no weighing scale with me, but I thought the coin seemed on the light side.
By that time I was certain I had bought a Bulgarian cast.
So I flipped the coin over and looked at the edge for a casting seam. Sure enough, there was something which looked like a seam, but after looking closely it seemed the coin was wrapped in something else. It turned out the seller had wrapped the coin in aluminium foil, which had taken on the details of the denarius from being compressed during postage.
That was a lesson in my own preconceptions. The coin in question, a denarius of Domitian from his short-lived monetary reform (82-85).