Verifying Authenticity after Purchase?

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Hello everyone. I am a new member and am looking to purchase my first Rolex. This is a wonderful source to learn about the great Rolex Brand.

What is the best way to verify authenticity? Would an AD have to take off the back to verify the movement. I am considering a purchase from a trusted seller here. Many sellers claim that they provide a warrantee card stamped by an authorized dealer.

Also, what should the letter series be for a new 2010 factory fresh watch? Can the manufacture date be determined from the serial number. Couldn't find this information here:

http://www.rolexforums.com/showthread.php?t=8478

Thanks in advance for your replies.