This is based on a true story.
"Selling Isobel" has since been retitled as "Apartment 407".
The sequence when Isobel enters the apartment is based on the real experiences of Frida Farrell, including the part where she was forced to wear used underwear for women.
Isobel (Frida Farrell) is seen bound and gagged twice. This has never been mentioned in the Farrell's real-life story.