[Grim_]

Why would you use sscanf with just one parameter?

pawn Код:

dcmd_land(playerid, params[])
{
   new ap, name[ MAX_PLAYER_NAME ];
   if( isnull( params ) ) return SendClientMessage( playerid, 0xFF0000AA, "USAGE: /land [ls/lv/sf]" );
   GetPlayerName( playerid, name, MAX_PLAYER_NAME );
   if( !strcmp( params, "ls", true ) )
   {
      // Landing at los santos
   }
   else if( !strcmp( params, "lv", true ) )
   {
      // Landing at las venturas
   }
   else if( !strcmp( params, "sf", true ) )
   {
      // Landing as san fierror
   }
   return 1;
}

And the original problem is caused because you return 0 at the end of command. You only need to do that in OnPlayerCommandText callback.