There's no doubt it's a fake. I believe the reason Cervelo/Castelli and other corporations don't go after them is twofold. I don't think the the laws that govern trademarks/patents are the same or as easily enforceable in those countries. Any law(s) broken likely occurs when they ship said item and it enters the USA. However, it probably isn't worth the time, effort, and $$ to go after them.
Compare the jersey from PBK in this link with the one on ebay and you can see the differences. Enlarge the photo on PBK and compare it closely side by side with the fake.