The salesmen didn't get $9, they paid it, which is why you can't just add the two to the 27. There are several (equivalent) ways to look at it and see the conservation:
amount to start = sum of end amounts
30 = 3*1 + 2 + 25
sum of changes = 0
(+2) + (-9)*3 + (+25) = 0
amount paid = amount received
9*3 = 25 + 2
etc ...
Or maybe the bell boy just dropped the other dollar on the way to the room