To start with, you have two options. If the address on the payment confirmation that you have been informed that you need to post the item to is a UK address then you could just post the item out, although it would be best to ensure that you use a fully tracked postage method so as to ensure that you can challenge any Item Not Received case that may be opened against you. If the tracking proves successful delivery to the address you were given on the confirmation of payment e-mail then eBay would decide the case in your favour. If, on the other hand, you do not wish to proceed with the sale, then cancel the transaction, citing "Problem With Buyer's Address" as the reason why.
Should you decide to cancel the sale make sure you add the buyer's User ID to your Blocked Bidders List, which can be accessed by clicking on this link https://offer.ebay.co.uk/ws/ebayISAPI.dll?bidderblocklogin. Add the buyer's User ID to the big white box that appears on the screen, click on the Submit button beneath it and the buyer in question will not be able to purchase anything else from you in the future.
In order to prevent people from overseas from purchasing items from you update your Selling Preferences to block buyers with a primary address in a country that you do not post to. To do this go back to your My eBay page, click on the Account tab and when the next page loads up click on Site Preferences. When the next page loads up scroll down to the section entitled "Postage And Packaging Preferences" and click on the link beneath that heading which reads "Postage Preferences." A new page entitled "Manage Postage Settings" page will load up.
Once the Manage Postal Settings page appears on the screen scroll right down to the bottom of the page and you'll see a section that reads "Exclude Postage Locations." Click on the Edit link to the right of that line and a new page will load up. The top half is for the various regions of the UK, whereas the bottom half of the page is for International destinations. Scroll down to the bottom half of the page. To block an entire continent tick the main box next to that region; however, if you only want to block some, but not all, countries from that area click on the "Show Al Countries" link and a big drop-down menu will appear. Tick the boxes next to all of the countries you want to block, whilst leaving the boxes blank for countries that you don't mind posting to. If you just want to block every single country in that region just use the main box instead and it will automatically block every country in that region. Repeat the process for every other region in the world until you are finished.
Once you have finished blocking the countries and/or continents that you don't want to post to scroll down the page and look for the sentence that says "Also Apply To Current Listings." Tick that box and once the updates are saved the changes will apply to all of the items you've already got listed for sale.
Finally, scroll right down to the bottom of the page and click on the blue Save button. From this point onwards any updates that you made when you were blocking certain countries and/or continents will apply to all of your current and future listings, and any buyers living in the countries you've decided to block will be unable to purchase anything from you.
