Mine were transcribed on a mainframe computer system that records times in a way that is almost impossible to alter. That turned out to be a big factor. Find a lawyer who understands that his or her job is to vet your copy, warn you of the risks and offer suggestions rather than simply attempting to persuade you to excise the troubling content. Tape sources and get them to sign a statement agreeing that the interview you have taped is true. If you take pictures, show the sources their photos and get them to approve.
Surprises are painful.
Figure out how you will pay for the eventuality of suit. Weigh your risks. Don't risk more than the information is worth. I would, first and foremost, be certain to verify all information you are given, even to the point of obtaining corroborative statements from at least two sources, especially where more sensitive or inflammatory matters are concerned, and document those sources religiously. At one time, this was standard journalistic practice, but has, as we all know, been supplanted by the desire to disseminate information immediately, with little regard to its accuracy.