So, at this point it is not possible to sell a complete curio.
The only way to get rid of a curio is to trade it to someone else for another complete curio.
To me, this seems more than a little strange. Part of the whole charm of collectibles is being able to collect, build, trade, and sell them on to others. Or, heck, even to help build and share the collector's spirit with others!
Further, let's say you have all of the enchantment curios, all of the travel curios, and all of the DMP weakness / resistance curios. If you've made a duplicate (because, you know, you did not know you couldn't actually get rid of it), you are forever more stuck with that duplicate. You cannot break it down, you can't give it away, you can't sell it... so you will always have two of one of the curios.
I just don't get the reasoning here. Once upon a time you could sell pieces and complete curios both, but that was taken away due to an exploit with curio pieces. However, such an exploit is just not possible with complete curios. You can't break them back down again into component parts. They will forever be complete, so, what's the harm?