It is sometimes the case that the tasker will, either overtly or covertly, tell the viewer what findings are desired. This situation is usually easy to detect, since there will be a degree of forcefulness involved. Either the tasker has as a preconceived belief and wants it to be confirmed, or may have some hidden political agenda which would be best served by certain findings.
In such a case, it becomes the project manager's job to deal with the situation. If the viewer is working the project alone, there is little which can be done except to recognizze that the cuatomer wants you to find some predermined thing, and will be very unhappy with you if you don't find it. In such a case, you may want to reconsider taking the project.