The provocative new book "The Real Estate Agent's Field Guide" by Bridget McCrea seems to be aimed primarily at new real estate licensees. But it is also a "must read" for every realty sales agent who is serious about the business and who takes a long-term view toward thriving and avoiding costly realty sales pitfalls. The book places heavy attention to the results of residential sales commission "compression" and how it affects the industry. Compression means reduction in the traditional 6 percent or 7 percent commission rate. Purchase Bob Bruss reports online. McCrea explains the trend is toward discount brokerages and flat-fee firms such as Assist2Sell and zipRealty. She says this places pressure on traditional brokerages to adjust their commission rates downward due to competition....