Since Brexit you may find them less keen to deal with the tax/paperwork aspect, the VCR act doesn't apply to a dealer outside the UK so door to door is not a problem.
If the cost is less than £135 they collect the vat at point of sale & pay HMRC, if the consignment is over £135 you buy it vat free from them but then HMRC claim the VAT at point of import,
That is paid by Royal Mail/Parcel Force, because they have the contract, who then bill you including their "admin fee".