The Pain Lusters

Washed-up young actor goes to work at a "cathouse for masochists." Criminal hijinx ensue. Cover copy reads: "Sin-sick minds demanded shame-tortured bodies!"
The set-up is similar to the Loren Beauchamp Another Night, Another Love: an out-of-work actor in his late 20s, Nick, his TV & stage days slowing fading, needs money, & is approached by an old acting pal who recruits him for male prostitution: in Another, it is loving up rich older women at a resort; in The Pain Lusters, it's beating up rich older women with a taste for pain in an outskirts NYC mansion that caters to the wealthy & sexually weird.
Nick slowly gets into the job—he has to audition for the madame, of course (the girlfriend of his pal), & learn the finer points of BDSM (L.T. Woodward, Silverberg’s doctorly pen name, provides a sort of preface, taken from Sex Fiend). The men & women of the pain mansion aren't mere mindless, soulless whores, but people with lost dreams & future hopes, each in need of finding love as any human.
All seems to go well until one wealthy woman, Carolyn, comes to the mansion seeking to re-experience a rape she endured three years ago, when a burglar broke in while her husband was away & ravished her by force. She claims it's the only time in her life that she had multiple orgasms & felt alive (as any real psychosexual researcher will tell you, there are these instances, fueled by the forced ravishings of romance novels). When Carolyn’s husband gets wind of his wife’s secret desires, he stakes out the mansion, gains entry & causes all hell to break loose.