The study was led by organisational psychologist Francesca Gino and is covered by the BPS Research Digest:
Dozens of students were asked questions about American history and received small cash prizes for correct answers. The students were either given the option of receiving advice on the correct answers, or advice was imposed on them. Sometimes this advice was free; other times it was paid for out of the students’ winnings.
Crucially, the advice always came from the same source – in the form of the answer that a student from a pilot session had given to the same question – so the quality of advice was held constant regardless of whether it was free or paid for.
Throughout the study, the participants took more account of advice they had paid for than advice they were given free, even though it was made clear to them that the advice was of the same quality. A final study showed the students took even more account of advice if it was made more expensive.
The full text of the study is freely available online as a pdf, although if you’re not convinced of the findings I’m sure Dr Gino would be happy to supply an additional copy for a small fee.
Link to BPSRD on the behavioural value of expensive advice.