Reputable Pre-Owned Dealer

[Bassplayer]

I am new to Rolex and looking to buy a late model TT Blue Sub or TT GMT - can't spring for a new one and want to make sure I don't get ripped off.

Please share your experiences if you have purchased pre-owned and who the reputable shops are.

Also, is there a "blue book" reference that I could use to make sure I pay a fair amount for both parties?

Lastly, any experience with http://preownedrolex.com/ ?

Thank you in advance.
Eric

p.s. - any idea why I can not post in the classified section?