With Booking.com the commission is 12%. The guest pays us for the room when they check in (eg $140). Booking.com takes the commission of $16.80 from our account each month on or about the 16th of the month.
Wotif's commission is also 12%. Wotif customers pay $140 to Wotif. Wotif supplies us with a Virtual Credit Card for payment in the amount of $123.20, which we put through when the guest checks in.
Our channel manager (Hirum) has a selection of OTA's attached and the commissions range from 10% (AOT, Expedia, Quickbeds) to 15% (Agoda, Check-in.com, Jetstar, Needitnow)