Graham Gibbs at the University of Huddersfield has a number of very useful YouTube videos on research methods, particularly focusing on qualitative research. In this video, he discusses transcription for qualitative research and some of the issues involved in this.
Some of the other points discussed in the video include:
Who should do the transcription - yourself, a professional typist, or speech recognition software?
Interviewees' disagreement with statements in transcripts
Potential sources of transcription errors
Transcript formatting - e.g. labelling speakers, anonymisation, structure, levels of verbatim
If you're interested in downloading the PowerPoint from the video, it can be accessed on the Online QDA website at the University of Huddersfield.