'Sex Work' by Frederique Delacost and Priscilla Alexander.
'Tricks and Treats' by Matt Bernstein Sycamore
'Diary of a Manhattan Call Girl' by Tracy Quan
'Madam: Inside a Nevada Brothel' by Lora Shaner
These are all American books, but you should be able to get them on Amazon. The first two are non-fictional accounts written by sex workers about their jobs and client.