Now the question is that how these maps play out ?.
Bugs ?. Balance ?. And all the things that come out when map is released as beta.
Good questions but ask yourself this. Given the complete lack of interest in custom maps from the majority of the server admins. and general player base, do you think the mapper has garnered enough feedback from players to address bugs and balance? And has he then been able to edit the map and make multiple changes (based on real player feedback) that he then tests again and again with even more players? On a full server? If yes, then there's a decent chance that it could be bug free and balanced.
But what if he has suffered the fate of most custom mappers instead? What if he hasn't received a bit of feedback or comment from real, live players? What if he's been sitting in front of his computer for the better part of a year working and re-working a map that he can only test with bots? What if he's lucky to have played the map with ANY live players (much less a full server)?
Now ask yourself these questions:
Would you still expect the map to be bug free and balanced?
Would you refuse to play the map because of a glitch in a texture or a misplaced spawn protection volume or some other "un-polished" issue with the map?
Would you not play the map because one team seems to have some sort of advantage over the other?
Would you stop playing the map because every time you join a server featuring it there is another new, edited version to download?
Would you still join a server if there were only 2 or 3 people playing the map?
Making custom maps is hard. Getting it to the stage where it's bug free and balanced is even harder.