This is exactly how it works in the UK for purchases worth £135 or less which are shipped directly from outside the UK. The retailer has to charge UK VAT as if it were a domestic sale at the point of sale, and there is then nothing to pay at customs so no hold-up for that. It's only consignments worth over £135 where it ends up being stopped for payment at import.

On top of that, Amazon and other large online retailers also have a huge distribution and warehouse network domestically in the UK already so for higher value items mostly they import themselves to their warehouses before sale and then sales are purely domestic.