Customer complaints are considered “indirect” when they “come over the transom” meaning they are not given face to face, no one is being interviewed or participating in a focus group. If a customer registers a complaint as a personal response to a request for feedback, interview, etc. that would be direct.
As an “indirect” example, a customer might receive hotel room service an hour late and, as a result, leave a scathing review on a comment card. But if that same customer was greeted by the General Manager in the morning by the elevator and the manager asked, “How was your stay?” You would most likely get a different response. Just the fact that the manager asked about the guest’s well being changes the nature of the feedback.
The goal is to mix “direct” methods where the customer is more conscious of how their words are being received, with indirect methods where they are unaware of who’s watching, listening or reading their comments. Think of how candid people can be on the internet behind the “veil” of anonymity. When capturing the Voice of the Customer, you are always searching for the most candid, usable feedback.