Ahhh the memories of getting a conch shell in Nassau.
About 20 years ago, back in the Big Red Boat days, my parents and I took our only cruise. We thought it would be great to get a conch shell near the dock on the way back to the boat. Bought it and brought it back to the room on board.
Fast forward a few few days later to the flight home to CA. About halfway into the flight, my Dad started smelling something around us. No, not that. I was thinking he was losing it. Over the next couple of hours before landing he kept on it saying something stunk.
After landing, we opened the overhead and knew something wasn't in good shape in our luggage. The second we were in the door of our house, my dad got a bucket of bleach, dumped it in and tore open the bag with the conch shell in it. He nearly fell over from the smell. In went the shell. A few seconds later he pulled it out and plop! Went a little piece of a conch.
Despite their insistence that the seller had cleaned it all out, he missed just a bit. Needless to say the luggage was in the trash. However, we did keep the shell for about 15 years.
Hopefully you can find one that is truly clean and will enjoy at home.