China : Whether you order a single mod or a life-size aircraft carrier complete with airplanes ( some assembly required

) , it's always 'electronic parts' and $4.95 on the customs declaration...
Which customs knows too - so they aren't buying into that anymore. Now they ask for proof of payment 'cuz they wanna see what you actually shelled out for the goods delivered.
Though it looks like Brexit's a done deal, EU regs currently still apply.
Reputable vendors will be wary of selling. If HM Customs and Excise catches on, they might put that vendor on their sh**list and reject/freeze his legit shipments too. Anyone in the market for the long run won't risk his business that way.
Other suppliers might play along - and will ask advance payment in full.
Had my indirect lesson about that while clearing a shipment of hardware from China :
Overheard the one side of a phone conversation of the customs officer with someone who had bought a pair of branded running shoes from China. Obviously fakes. Gist of the conversation: Money gone (upfront payment), shoes impounded , importer lucky as only a single pair. Two pairs would be viewed as commercial import which would have resulted in a notice to the trademark owners - or rather their lawyers....
Nope, me gonna keep me nose clean...
What again were the freezing/boiling points of nic, pg and vg ? ...