Is it possible to fake being a top rated seller on ebay with 99.7% positive feedback out of 3990 customers?

Yes it is. I've heard that foreign ebay users (especially china) rate each other (people they know/possibly themselves in other accounts) continuously.

If you look at the feedback there are, they're usually in broken english and only a couple of word at a time. Then every once in a while there will be a negative feedback with correct grammar and capitalized words instead of 'fast service great quality'