If both items were paid for on the same invoice then the seller has done nothing wrong, the total cost for two purchased in one go was clearly stated. It doesn't mean I think they deserve any credit but I would certainly mark their postage cost star as 1.

As soon as I saw that I would either have hit the back button or, if I really wanted them I would have purchased one, paid with Paypal and then gone in and bought another later, preferably changing the delivery address to a friend or relative, so at least they could not make a few extra bucks by sending them together.

As you purchased the two items at the same time and not separately that is considered one transaction.

They would have been paid for together and therefore they are posted together. The seller has done nothing wrong sending them in the one parcel.

Shipping is clearly showing in the listing and the shipping cost would have shown even before you made the purchase so any questions should have been asked prior to purchase.

I am not sure how the USPS charge but if I am sending internationally there is very little savings on postage when combining items.  The same may apply to parcels coming from the US to Australia and you may find the seller really hasn't made a profit on the postage side.

I agree in part, but that said, the seller should have sent 2 parcels.

If there is one payment for both items than the items should be posted together. If the items were paid for via 2 Paypal payments then they should technically be posted individually.

The issue is also the system, and lack of understanding by many on how to purchase and pay for multiple items.

By way of example I once had a buyer purchase multiple items and pay for each individually as soon as they bough the items. The end result was that the amount of postage overpaid was in excess of $75. I combined the entire lot into one parcel and posted it and refunded the buyer the $75 in postage as I believed that was the right thing to do. It of course cost me a Paypal transaction fee for each sale so I in fact ended up out of pocket. I had my fingers crossed that the buyer was honest as they could have easily opened a Paypal Item not received dispute and they would have got a refund for everything I sent them. The alternative was that they may have left me negs and low DSRs all round if I "followed the rules" and posted everything individually as they obviously didn't understand how to combine their items by requesting a payment total before paying etc.