It says this: All specifications listed are subject to change without notice.
Right on the page you link to. The above is a copied quote from that page.
Giant is the biggest(of LBS bikes) frame builder in the world, they don't misrepresent what they sell.
AND, if you were going to sell a fake wouldn't it be smart to emblazon said fake with the real brand logo. For instance fake Rolexes generally say "Rolex" on them somewhere.
AND, the bike you are looking at is a 2006 model?
AND(A BIG AND) your first sentence says the bike is USED(For those not in the know, this means someone else has had possession of the bike and might have even ridden it or changed something about it. It might even have different tires. Watch out, they might be fakes). Maybe the owner changed the brakes, maybe he removed the logo, maybe they are not Shimano brakes. Why don't you ask the seller?
The part number for a Ultegra caliper is BR-6600 which means nothing because a decent fake would have the part number cast into it anyway.