Would-be novelists are always told: write what you know.
What this actually means is that you have to look like you really know what you're writing about. Which can lead to interesting situations.
In this week's Phil the Shelf, novelist Mark Keating reveals how he goes out on his piece of north Pembrokshire, primes a flintlock pistol with gunpowder... and, er, fires it.
Apparently, even though it's a handgun, this is not against the law if no-one gets shot. And if you did try to rob the local post office with a flintlock, it probably wouldn't take Dyfed Powys police all that long to wrap up the inquiry.
The point is, knowing how to go about shooting someone in the 18th century is quite important if you're writing novels, as Mark Keating does, about pirates. Real pirates, that is, many of whom were Welsh, although Mark's principal character is Irish. Cross of Fire is his fourth novel about Patrick Devlin, and finds him in search of legendary treasure off the coast of Africa.
It's all deeply-researched, because authenticity has never been more important for a novelist - and the internet, as usual, might be to blame.
In the old days, it would usually need a trip to a reference library, but now it couldn't be easier for a curious reader to check on a writer's sources, find out which bits are factual and which have been made up. And - even worse - which 'true' information has been bent to shore up the plot.
Bad enough for writers of historical fiction, even worse if you're working with contemporary situations. A native of Cardiff tells me that even the great John le Carr茅聽made a fundamental error relating to the city's geography in his latest novel, A Delicate Truth.
Oh, yes, truth is delicate all right, and writers are constantly looking over their shoulders. Thanks to devices like Google Earth, assiduous readers can now follow your story on the ground.
You have a guy dive into a convenient doorway to avoid his pursuers and someone in San Diego emails to point out that there are no doorways at the southern end of this particular street in Swansea as all the buildings have been demolished and the site turned into a car park.
A minefield. Thrillers are particularly risky, especially if they involve police procedure. New criminal investigation divisions, identified by very forgettable acronyms, are appearing every other week. And terminology is constantly changing.
At one time, the people in plastic suits who sprinkled powder around murder victims were always known as Scenes of Crime Officers - or SOCOs. Now the Americanism CSI seems to be creeping in. And murders - British murders - can now officially be referred to as homicides. What's the world coming to?
Even archaeological procedure is becoming more technical and rarefied, with the increased use of ground-radar before you even get to take down the trowels.
Not a problem for our second guest, Francis Pryor, director of many digs for the late lamented Time Team TV series.
Francis has written a bunch of acclaimed non-fiction books about the landscape and what lies underneath it, and his first novel, The Lifers' Club, featuring archaeologist Alan Cadbury, is a prime example of writing about what you know. Getting it published, however, has been far more complex, as you can find out in the programme.
Which is the last in the series, by the way - although we'll be back in the autumn.
Listen to on tonight from 6.30pm.