I think you mean that only the _seller_ pays the agent. But yes, I agree the American system is a bit odd. For one thing the listings are WAAAAYYY old by Australian standards - here you list your house with an auction or "sale by" date usually six weeks in the future, and ... it sells (usually). It looks to me like the American system has longer listings because there are fewer open-house inspections - your buyers agent arranges a time to inspect on your behalf, or something like that?

Yes you are right - the buyer pays the agent.

At the moment is Sydney properties are selling off market which means 0 day sales. The time it takes in the USA seems amazing long.

You don't need to use a buyer's agent, but it's usually a good idea to have someone at less theoretically looking out for your interest. If you use the seller's agent, that one agent has a big conflict of interest. If you have a real estate attorney (which isn't very common in california, but may be in Australia), then I wouldn't see needing an agent as well.

Yes in Australia as a buyer you will have your own lawyer looking over the details once you buy. The problem with buyers agents is their interests are rarely aligned with your own.