Agency remuneration can be extremely complex and tricky to follow - like airline remuneration this is possibly purposefully so. There is an argument that since airlines commoditised fares by putting them online as combinable one-ways, millions of dollars have been left on the table. In reducing costs many have also reduced revenues.
Base commissions, also known as point of sale commissions, are typically paid by carriers via the BSP (Bank Settlement Plan). Overrides come in several forms and are typically paid based on 'flown revenue' (airlines claim revenue when the sector has been flown rather than when a ticket is issued) or volume targets or other.
Domestic commission is extremely low - but then again it's typically a commodity transaction that can easily be fulfiled across the web. Trans-tasman is counted as domestic by some (QF, NZ, DJ) and international by others (EK). International base commissions vary from 5% up to 13%+. Overrides can add several more % points, but you have to harness significant buying power to tap into them.
The only hope for your favourite travel agent is that they provide a value-add service that you can't easily DIY on the web, such as manage corporate travel consistently, or search out tricky combinations of fares, accomm and tours. Ironically, most research still shows that agents and the web are priced about the same (of course there are isolated exceptions).
Next, they have to charge some form of service fee, whether that's declared on top of a ticket, or as part of the hidden margin they add to a package. If they're not doing either of these, expect to see problems for them within 2 yrs....
Apologies if this is too much detail but sometimes it helps to understand the economics a bit more.