Ok, can anybody think of any modding tricks that could be used or glitches that could be exploited to trick the game into thinking that an entire level is part of a brax shop? It just occurred to me that if a way could be found to do this then it would make it possible to sell items anywhere.
The game checks it on a per-room basis, so the only way to achieve that would be to make every single room into a shop. That, or make giant elaborate rooms which encompass the entire floor all at once. But really, I have the feeling that it would cause something in the game to explode. Do try if you are feeling brave, though; maybe you'll succeed.