Seller suggested £600 post to Australia, I read that as "CBF".

In the HMRC website's condensed tariff PDF there isn't a listing for towbars. That aside, I have no idea how much of a pain it is to receive goods from another country if you live in the UK - have only ever sent things as accompanied baggage. What's involved - does the post orifice or freight company simply say "Pay £XXX NOW" or do you get a notice with the option of DIY declaration (assessment)?