We use Transferwise all the time to convert as we need between USD, GBP, and EUR. They are regulated. Registering with them requires photo ID (Passport or Drivers license).
They do offer bank transfers via their interface.
If we convert GBP to EUR for example the money moves from our UK bank account to Transferwise instantly ( the UK offers instant bank transfers), has a tiny fee deducted, converts to EUR at spot rate and hits our Spanish account in about a half hour. GBP to our USD account ( in the USA or in Spain) follows the same procedure but takes a little longer ( 24 hours).
Transferwise is a highly cost effective way to convert between currencies.
For this to work you would not need to open an account with Transferwise (desktop and / or app).
You would give your guest your bank account details in the USA (or wherever) - account number and routing number / SWIFT code - your guest then purchases USD via Transferwise with AUD and the USD goes from Transferwise to your account.
If you opened an account with Transferwise you would instead give your Transferwise account name and account details. The AUD would convert to USD pass into your Transferwise account and you can then transfer the USD to your USA account.