How to sell a room in a communal apartment profitably?

The problem is that a room in a communal apartment isn't the most liquid asset, so "profitable" is relative here. The main thing is getting all your neighbors to agree to the sale (or at least not be against it), otherwise you'll scare off a buyer once they realize who they'll be living with. It's best to search locally - through listings, acquaintances, neighbors - because most people are only interested in a communal apartment if it's in the right neighborhood and close to work. And remember, buyers will evaluate less the total area and more the size of the room itself, whether it has a window, and the condition of the common spaces.