It is a reality on Ebay and Amazon
40%+ of all sellers of electronic tat are in China, pay no VAT and try to pass their packages as "gift" in their customs declaration.
While this should be enforced at import by customs, the sheer volume will overwhelm them so we will have to find another way and making Amazon and Ebay _WITHHOLD_ VAT AND CUSTOMS FEES/EXCISE to any non-Eu seller which exceeds the VAT registration threshold is the only way. They have the full information needed for that - namely the annual turnover of a particular seller, its out-of-Eu jurisdiction and they are the conduit for the money.
Now why Customs and Excise is not requesting this from Amazon and Ebay - well, there is a reason why Amazon and Ebay pay that much to various lobby groups :)