THE LAUNDRY BASKET!
So how does it work? You donate a common to the laundry basket, and it will spit another one back out at you! What it could be is a complete mystery, but I will try and make sure they are roughly in the same price range (so you’re not getting stockings in exchange for fairy wings XD).
Just send the Llama a trade, making sure you put that it is for the laundry basket in the comments, accept it, and wait for your item! Please, keep it to like... 2 or 3 times a week.