Ok thanks. So nothing the seller would know about or deal with.We have left the EU, as a result you will be required to pay VAT on any items purchased. Typically the delivery company will text/email you a payment link once its entered the UK. Basically add 20% to anything you order, and before you ask ... no you wont be able to get away without paying.
Well they likely have an awareness of the new rules unless their super bespoke/small org, but from their perspective they would just ship it and leave the rest to the delivery firm to deal with.
Should also point out that the delivery firm will also add on a 'handling fee'. DHLs for example is 2.5% of the VAT and a minimum of £11.00.
This link is pretty good at explaining it all.