I've been looking through some of the threads and noticed that people mention getting glory points for selling three of a good in demand. I can't find anything in the rules for this. The only time I see you get a glory point for gaining gold is when you plunder 12+ gold from a merchant ship. Am I missing something?
Yes, you seem to be missing page 3 in the rulebook
Glory Points are awarded to players every time they perform various acts of glory and infamy:
• Defeating a Player or NPC
(Defined as surviving and winning Naval or Crew Combat)
• Selling 3 or more Cargo Cards in a port where the goods sold are ‘in demand’.
• Plundering 12+ Gold in a Merchant Raid • Completing a Mission
• Finding a Rumor to be true
• Buying a Galleon or Frigate
(only once per Captain)