[Gazereths]

You have to prove what the thing being posted was worth, invoice, receipt, ebay auction or whatever. You're insured up to the maximum amount of the policy taken out. The declared value might come into play but you can always argue that you had no knowledge of what the sender declared, or that it was a mistake on the form. Also the carrier, not the customs office would deal with the claim. It's very much a grey area and a risk you have to weigh up.