Which is what they used to do with the blanket charges under their Global Shipping scheme.
Used to? They still do. GSP charges way more than the 10% GST owing on purchases into Australia. I ignore EBay listings that use GSP. $30 to ship a farthing at snail pace? It's laughable.
I suspect you in the UK are facing what happened in Australia some years ago. With increasing OS sales certain millionaires whined that Australians weren't buying from them because of the 10% GST they had to pay in Australia but not from overseas. To appease them the government decided to implement GST collection on OS purchases. Problem was, how to collect it? Both customs and Aus Post got their backs up and modelling showed that the cost of collecting the GST using these methods would exceed the amount of GST collected. As a solution the government decided to make electronic sales platforms (and I think freight companies) responsible for collecting the GST. Legally they had no jurisdiction over international companies so they could give the Aus government the finger but companies with a physical footprint in Australia (like EBay and Amazon
) were soft targets. In Australia you are liable to charge GST if you have an annual turnover of $75,000AU (whether you sell new or secondhand items) so technically, an overseas company that does $75,000 of sales to Australia should pay GST. Never going to happen though. So yes, many OS sellers would be under that $75,000 limit but it's too much hassle for Ebay and the likes to weed them out so they place a 10% charge on all OS purchases. The irony is that many items purchased from OS are not available in Aus or are still way cheaper (including shipping) than the same items for sale from Aus sellers so I suspect the introduction of GST on sales platforms hasn't bought droves of punters back to buying from Australian sellers. We are still lucky in that the post office doesn't perform customs duties so most packages ordered directly from sellers don't get charged GST.