Taking the Dandy Archetype Dedication Feat should give expert in Diplomacy and Society, but it seems to be giving expert in Deception instead.
Hi there! Dandy indeed gives expert in Deception, according to it’s description:
You become trained in Deception and Society; if you were already trained in either, you become an expert in it instead.
This is consistent with the printed book (Player Core 2):
:facepalms to the moon and back:
I tunnel visioned hard on the “prerequisite: trained in Diplomacy”. Apologies for the misreport!
No worries at all! I did have to read it like 5 times as I replied just to make sure, so I think it’s an easy mistake to make. 
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