My T-100 from 1966 (Hoboken, NJ) has the serial numbers recorded twice on the guitar: an impressed stamped number on the rear of the headstock and again on the label, inside the guitar.
I enlarged the photo of the ("your") guitar greatly, and while I do not see a serial number on the headstock, I'm sure I can see the oval, tan paper label glued inside the guitar body. You can see this through the upper "f" hole. I can see part of the wreath pattern that is printed on the border of the oval paper.
So, contact the dealer and simply ask him what the serial number is. That label will have it, as well as the model of the guitar, written by hand on that label. He will know where to look.
----------------------------------------------------
OK, so once you get the serial number, you can find the date/year it was made, and generally confirm the authenticity of the guitar. Go to this site and download (via link) the PDF file that will allow you to date the guitar:
http://www.guildguitars.com/index.php/support/dating/