Originally Posted by Sasik

It isn't good idea. You should announce the map at least one week before the match. You won't be suspected of any machinations then. Why? Well, your idea can make situations like this:
'Clan A: OMG, THEY (clan B) KNEW EARLIER THAT TEH MATCH WILL BE PLAYED ON SBV2!11 (for example).
Clan B: O.o WE DID NOT, YOU LAMES, NOOBS!111 (etc.).'