After finishing A Book of Tongues, I looked at Soiled Doves and went, "You know, I bet Gemma Files read that in her research."
That said, it's one of the worst pieces of nonfiction I've ever goddamn read. Not particularly nuanced or well-written to start with, it is staggeringly judgmental (perhaps the title should have tipped me off) and in desperate need of a proofreader. Rather than presenting the information and letting the facts speak for themselves, Seagraves feels the need to sprinkle her prose with language that would sound amateur even in fiction — despicable! sordid! degrading! — and enough references to "iniquity," "sin," and "the ugliness of raw, naked vice" to make it clear that she's not just offering sympathy for the prostitutes' bad working conditions, but also judging the hell out of them for it.
In conclusion: lousy writing, and so badly biased that it makes the content suspect.