If we're talking about single items here, the customs here doesn't give a rip about anything but the value. You can't put zero value on something here and have them not sniffing at it. And then when it's opened they only care about seeing an invoice. Most ebayers forget that part, and that's why I always have to print out the Paypal receipt. If the value is different on the customs form, they're not really bothered about it, as long as prove with the invoice how much it's worth, and pay the customs on that.
What they're after are the big-ticket orders that are clearly not legal, like shipping a bunch of computers and marking it as "used, gift, zero value." Or thousands of cd's, or things even less legal...
But one person ordering one thing? No, they won't come and arrest the sender or sendee, they just want the tax on the value of the invoice.