Typically, eBay only requires you to provide the original sales receipt for high-fraud-potential items. For example, when a new "high tech gadget" is released (like the latest ipod, xbox or wii), eBay has to set special requirements for sale, to stop rampant fraud. They frequently require things like showing the original sales receipt, and showing a unique photograph of the actual item (as opposed to a stock photo) to weed out scammers.
Unfortunately, it sounds like you must have triggered the anti-fraud algorithms, and the only way to get through this is to comply with the requirements you are given.
The fact that you have almost no experience as a seller (only 12 selling feedbacks, and all received in the last 5 months) and you have over $13,000 in listings (current and ended in the last 2 weeks), explains why. You haven't proved yet that you can handle that much business.
Once you have gained more experience, and proved that you can deliver the items and provide good customer service, you will find that the restrictions are gradually eased up.
