1. I don't live in the UK.
2. It doesn't matter what the value is online because it doesn't prove one way or the other how much you paid.
3. Customs can open a package in any country, but that doesn't have any bearing on this discussion unless you're trying to smuggle something not declared on the customs forms/manifest/invoice.
4. If they change the value or assess duty on a value not specified you can, in any civilized country I'd expect, contest this and hopefully get your money back by providing a copy of your invoice (and or payment receipt) if it wasn't already included with the package.
You want a practical example? I import a lot of stuff, including wholesale goods. Arbitrary example, but I may by a part for $2, add some value and turn around and sell it for $20. Checking "online" some customs monkey might find a store selling it for the $20 or even $50. That has no bearing on how much tax I should pay, as it's a $2 part when I imported it.
Sellers are responsible for putting down the true transaction price of the packaged goods and in many cases must attach a commercial invoice (depends on carrier). They're responsible for being truthful under penalty of law, regardless of what country they send from.
So if your package says $25 on the customs slip, but has an invoice attached for $250, then expect to pay duty/tax on the $250 because it's obvious the customs form is BS. If there's no invoice attached and you can prove you've been charged duty/tax on the wrong value, then call up your local customs office and get a refund.
People in some countries, such as the US, may find all this laughable because they have unusually nice exemptions. The US for instance, allows packages of commercial goods up to $200 in value to enter duty/tax free to a single address - one per day. Nice. Here in Canada there is no official min/max that I know of, so it's usually at the discretion of the customs officials and even more importantly, the carrier. In the past few years anything that's $50 or less hasn't been assessed any taxes when coming via post. But via DHL or UPS for example, it doesn't matter if it's $5 or $10, they will make sure you pay tax on it so they can collect their brokerage fees/commissions.
I look forward to seeing more pics as they show up!
