Do you have hot and cold running nonsense where you live?
Selling to Australians takes place in Australian dollars and the transactions are cleared by Australian banks. This makes them pretty easy to get a legal grip on.
And you will also find that the large companies who are doing most of the price discrimination have local subsidiaries which can be dragged into court without too much fuss. If they try something like yanking funds to avoid court judgements, they're violating various laws and privileges and our government can and would be able to seek enforcement from courts in the USA.
People think that trading across boundaries gives you magical immunity from national laws. It doesn't. Where you have a nexus with a country, you can be enforced against through that nexus. Where the laws are similar, brother courts will typically reciprocally enforce them.