Here's something I did to check my facts in The Pericles Commission: I cold called a professor of classical archaeology, one who specializes in 5th century Greece and Persia!
The basic idea should work for anyone. For anything from theoretical physics to the sex life of the lesser spotted boll weevil, there's an expert out there, and if you're very lucky, they'll be as kind as Professor Margaret Miller was to me.
Margaret not only answered my questions with the greatest patience and attention to detail, but she very kindly offered to read the entire ms. Which was generous beyond measure since she had her own academic book to write at the same time.
As she read, I lived in daily fear of an email saying something like, "Gary, you idiot, character X was definitely dead in 461BC." Or, "That building didn't exist then." Or, "Didn't you read Obscure Reference Z which proves your entire premise is wrong?"
Incredibly, I survived her check. (mostly)
Margaret did point out a number of errors and improvements, almost all of which involved clothes and furniture. You have Margaret to thank for the characters wearing correct clothing, and the description of Pericles' home office.
Any errors which remain in The Pericles Commission are all my fault, and I wish you joy of finding them.
An odd postscript to this: months later I was doing research for the second book, on relations between Athens and Persia, when I came across an interesting reference. I started to read. The book I’d found was very useful stuff. Wow! Who wrote this? I checked the cover, and it said, Athens and Persia in the Fifth Century BC, by Margaret Miller.
Thank you Margaret!