They may do this explicitly (by refusing to ship to your Australian address) or implicitly (by charging a shipping fee so high that it's not worth the time and bother to buy overseas).
Beat them with virtual credit cards
Geographically-based blocking of your Australian credit card can be a real pain.
Recognising the growing demand to be able to buy online around the world, a host of 'virtual credit card' (VCC) operators are offering prepaid cards that are not attached to actual bank accounts.
Instead, you simply recharge the cards with any amount you like, and can use the number on the card to shop to your heart's content.
In addition, many VCCs don't require an actual piece of plastic, but can email or SMS you the details for your card; the US-based globalVCard (www.globalvcard.com) is a good example of this — it's a smartphone app that instantly generates one-off MasterCard numbers for online shopping use.
The possibilities of this model are obvious and significant: get a US-based VCC, and your geo-blocking troubles are — theoretically — over.
However, it's an inexact science as most VCC providers are banks and only provide the cards to existing customers.
Australian providers like VirtualVCard (www.virtualvcard.com.au) sell through 7-Eleven and BP stores, but have the same geographical issues as conventional cards.
Third-party firms like US-based EntroPay (www.entropay.com) work outside the bank system and allow a US-based address to be attached to the card, which can trick some US-based shopping sites.
Others may require a US-based credit card number as verification, or require a US PayPal account (PayPal is a stickler about geographical location).
Choosing the right VCC provider requires looking around. In the end, it may be helpful to have an overseas friend or relative, or a shop-and-forward company that you trust, source a US VCC for you and send it your way.
The prepaid-only nature of the card means you can keep only as much on the card as you want to spend.
Rise of overseas shopping assistants
Such is the demand for overseas-based shopping that some businesses offer Australian customers a curated selection of products chosen from inventories of US retailers.
One is Australian venture Online Shopping USA (www.onlineshoppingusa.com.au), which has made its own version of AmazonGlobal by offering Australian customers a selection of products chosen by the company's staff from US retailers.
"We are constantly scanning those sites for the best deals that we can showcase to Australian shoppers," director James Harris explains.
"While a lot of people have been shopping online in the US, we thought there was an opportunity to bring together the best of US online shopping, and aggregate that all in one site.
"Customers have the guarantee that those retailers are genuine retailers, that they have been vetted, and that they offer the full range of services [to Australian customers]."
Online Shopping USA's agents can also buy products from US merchants, aggregate shipments, and ship products to customers in Australia.
Business for the almost 2 year-old venture took off in line with the American Black Friday and Cyber Monday online sales, yet even Australia's high-profile Click Frenzy event "provoked a lot of interest", says Harris, who notes that the most popular products includes runners, designer labels and electronic goods such as digital cameras.
While authorities and retailers consider who will flinch first, consumers are continuing to scour the net for the bargains and styles they want — and are proving to be more than willing to let someone else do the actual purchasing for them.
As a result, many Australians now have the same kind of relationship with their overseas shopping assistant as they might have with a local vintner or hairstylist: trust is crucial, and a good agent can become a partner-in-crime of sorts, in helping source the overseas products they want.