I had contacted Customer Service to ask them the same question so I'll tell you exactly what they told me.
Usually he never sends the Invoices, but if one of your Winned Gifts works more or encounters a malfunction, just contact them to send them the Gift and they will of course be charged the shipping costs.
A quick question to the webmaster about how to guarantee the gifts won (wii, ps3, xbox, ds......)? Can we have an invoice for example? Thank you in advance for your answer.