I am no expert but with 8 years in this industry and 11 years in the police beforehand I can speak from experience. Some clients do show signs of becoming a sexual deviant otherwise known as paraphilia.
Paraphilia (definition from medical dictionary)
Sexual deviancy Psychiatry A mental disorder characterized by '…recurrent, intense sexually arousing fantasies, sexual urges, or behaviors generally involving, 1. nonhuman objects; 2. suffering or humiliation of oneself or one's partner; or 3. children or other non-consenting persons, that occur over a period of at ≥ 6 months…(causing) significant distress or impairment in social, occupational, or other important areas of functioning; sexual excitement to the point of erection and/or orgasm, when the object of excitement is considered abnormal in the context of the practitioner's societal norms Formal paraphilias, per Am Psychiatric Assn Exhibitionism, fetishism, frotteurism, pedophilia, sexual masochism, sexual sadism, transvestic fetishism, voyeurism, paraphilia–not otherwise specified, a 'wastepaper basket' category Management Psychotherapy, antidepressants, progestins, antiandrogens, surgical castration, triptorelin.
Obviously this has to be taken in context what is considered normal by people within the industry maybe considered abnormal by the general population.