McQuarrie E. F. Customer Visits: Building a Better Market Focus. Newbury Park, Sage, 1993. [Very well written; the topic is somewhat specialized, but many of the points apply to qualitative research in general.]
If you want need a good marketing research reference text you might invest in Churchill's Marketing Research. It has everything (almost). Also, Churchill is the required textbook for 15.822.
Churchill, Gilbert A. Marketing Research, 6th Edition, Chicago: The Dryden Press, 1996. [Plus: Comprehensive and precise. Minus: Dry, expensive.]
Lehmann, Donald R. Market Research and Analysis. 3rd Edition, Homewood, IL: Irwin, 1989. [Plus: Well written, sensible. Minus: Virtually no coverage of qualitative methods.]