As a consumer, the best thing to do is shop around unless money is not an issue. I know for me, finding the best possible price is the only concern, regardless where I buy them from. I've gotten some steals on ebay, not necessarily for the Pani but both for my car as well as previous bikes. Only problem there is the potential warranty issues but then again, when buying from someone selling a used item on a forum is the exact same thing. DP rearset is the same item no matter where it's sold. If the price was right, someone would be a fool to buy from a dealer or even a reputable merchant if they could find the same thing from a mom n pop shop or ebay for half the price. Not saying this is the case but just an example.
Anyway, $900 shipped is still not a bad price. Just far too expensive for a rearset. Pretty good price for DP though.
GLWS