There will be an invoice on the outside of the box,they have to put this on by law,the problem is if you try & disguise it & they dont like it,theyll x ray it anyway! ,so the only way to to get around really, is to get the shipper the to mark the value down & put SAMPLE on the box,downside if it goes missing you can only claim for the invoice value! !.
Anyway,to calculate duty,you roughly add 10% import duty,then vat on the lot! ,so,£500.00 x 10%=£550.00 x20% =£110.00 duty,so total payable to customs is £160.00! .
Or if youre vat registered pay through ure Co,& pop it on ure return & hope you never have to explain when you next get a vat visit! .