In Lavender Beds (and I assume the other housing areas), there is an NPC, Resident Caretaker, that answers some questions. The question "Why are we not allowed to buy or sell used furnishings?" is selectable from the menu; if selected the following is said:

"Placing a furnishing will bind it to you, preventing future trade or sale to other players."

While I (kind of) understand the reason this restriction was put in the game, that line does nothing to answer the question asked. "You can not sell it because you can not sell it," is basically what it says.

I'm sure whoever writes dialog can think of something, probably something involving the flow of aether and the calamity. This just seems lazy...