In theory, yes the seller should have the ability to remove VAT before sending to the UK. However in practice, a lot of sellers aren't bothering as it's simply too much hassle for them, and for items under the £135 (?) threshold, they have to act as unpaid tax collectors for the UK government. Sadly a lot of sellers are unlikely to care if we get hit with double VAT. Another one of these Brexit bonuses we hear about, I guess.