I ship a lot of sales items to Europe, the U.K. and other foreign destinations... fortunately, the Ebay shipping system is quite sophisticated in the when the sale occurs, the system recognizes a foreign sale and when the shipping lable is printed, the correct declaration for the applicable receiving country is printed. The seller must declare what is in the package (automatically generated from the sale itself and then sign the declaration authenticating the value (also taken automatically from the sale data). All very helpful. Most of the items I sell are under $200 (average about $75 U.S.) and I ship exclusively with United States Postal Service... usually Priority Mail... only oneproblem in the last 2 years and that was easily resolved with the buyer (thankfully).
As an aside, most people, including yours truly until about 6 months ago) are unaware of an international treaty that was implemented on July 1, 1875, when the General Postal Union came into being. This title was changed in 1878 to the Universal Postal Union (UPU), and the basic treaty was renamed the Universal Postal Convention. The treaty provides a uniform framework of rules and procedures for the exchange of international mails.
Most importantly it addresses a question I had always pondered... how does payment of a postal fee in one country get "shared" with the recieving country. It just so happens that the shipping country gets to keep all of the postage... apparently it averages out for all countries involved...