Cognitive processing therapy (CPT) is an effective treatment for posttraumatic stress disorder (PTSD); however, some patients do not improve to the same extent as others. It is important to understand potential factors that can be modified for better patient outcomes. This clinical trial implemented a three-arm, equipoise-stratified randomization design to allow for the accommodation of patient preference before randomization to one of three CPT treatment modalities: in-home, in-office, or telehealth. This study examined whether satisfaction with the modality, perceived stigma, expectations of therapy, and credibility of the therapist differed between modalities and whether these factors impacted treatment outcomes. We hypothesized that the contributions of these variables would depend upon whether participants opted out of any treatment arms and that these factors would predict treatment outcomes. Participants who endorsed less perceived stigma demonstrated larger reductions in PTSD symptom severity than those with similar levels of perceived stigma in the telehealth and in-office conditions, η2 = .12–.18. Participants who endorsed lower satisfaction with their treatment modality and were assigned to the in-home condition experienced larger PTSD symptom reductions than those with similar dissatisfaction in the telehealth and in-office conditions, η2 = .20. The results show the robustness of evidence-based therapies for PTSD given that dissatisfaction did not impede treatment success. In addition, they demonstrate that it is important for clinicians to address stigma before initiating evidence-based therapies for PTSD. Strategies to address these factors are discussed.