This can't seriously be allowed right? You shouldn't be allowed to hold a map purely for the reason of selling it.
There isn't any official rule against this, but I agree that this is frowned upon to the majority of players in this server.
It's their choice. They own the map (provided they continue to train and use it) and are allowed to sell it to whoever wants to buy it. Not that I condone it - I hate map sellers and I love messing around with them.
It's the dumbest, most ridiculous way to make money. When I see someone's doing it I automatically think he's a jerk.
If you're training there and just finished training, but would like to make a bit of money on the side, I can see why you would, but if you just go to an empty training map and don't train and your sole purpose was to sell the map, not only is this a waste of time, but you could probably make more doing something else then looking for maps to sell. Make no sense financially and time wise.