I think the field of persuasive communication is relevant for your answer, as well as research into the efficacy of psychotherapy.

Customers trust advertising if it is communicated by:

• attractive persons
• credible experts

Psychotherapy is more effective if:

• the therapist believes that his methods are effective (!)
• patient and therapist share the same world view and values
• like each other

What constitutes attractiveness, expertise, common values, and sympathy, will differ among individuals. For some, expensive architecture makes a bank more trustworthy, for others it is a sign of waste and mismanagement. So you will have to identify the exact parameter value for each target group or, for perfect fit, even individual person. But basically what you have here are moderators that affect the efficacy of a placebo.

What is noteworthy is that the belief of the person administering the placebo has an effect. So it's better they don't know it is a placebo, but have been given it by a person they in turn trust.

There is a lot of research into both areas, I give only one introductory source each (both of which respectively include what I quoted above):

• Goldstein, N. J., Martin, S. J., & Cialdini, R. B. (2008). Yes!: 50 Scientifically Proven Ways to Be Persuasive. New York: Simon and Schuster.
• Wampold, Bruce E. (2001). The Great Psychotherapy Debate: Models, Methods and Findings. New York: Routledge.

Don't be fooled by the popular nature of the first book, Robert Caldini is an eminent expert on persuasion. If you want, there are more scientific publications by this author.

I think the field of persuasive communication is relevant for your answer, as well as research into the efficacy of psychotherapy.

Customers trust advertising if it is communicated by:

• attractive persons
• credible experts

Psychotherapy is more effective if:

• the therapist believes that his methods are effective (!)
• patient and therapist share the same world view and values
• patient and therapist like each other

What constitutes attractiveness, expertise, common values, and sympathy, will differ among individuals. For some, expensive architecture makes a bank more trustworthy; for others it is a sign of waste and mismanagement. So you will have to identify the exact parameter value for each target group or, for perfect fit, even each individual person. But basically what you have here are moderators that affect the efficacy of a placebo.

What is noteworthy is that the belief of the person administering the placebo has an effect. So it's better they don't know it is a placebo, but have been given it by a person they in turn trust.

There is a lot of research into both areas; I give only one introductory source each (both of which respectively include what I quoted above):

• Goldstein, N. J., Martin, S. J., & Cialdini, R. B. (2008). Yes!: 50 Scientifically Proven Ways to Be Persuasive. New York: Simon and Schuster.
• Wampold, Bruce E. (2001). The Great Psychotherapy Debate: Models, Methods and Findings. New York: Routledge.

Don't be fooled by the popular nature of the first book; Robert Cialdini is an eminent expert on persuasion. If you want, there are more scientific publications by this author.