If my textbook was a person, I would call them racist, pedantic and obvious.

The textbook got it right by showing no-one in the class. 

"Perhaps you want only one sample because you do not have the time or energy to draw many different samples. You are not alone." Thank god. I thought I was the only one who wanted only one sample on account of lacking the time and energy to draw many. This passage has eased my mind.

"Those without phones (e.g. the poor, the uneducated, and transients)" ...er perhaps a little harsh, Basics of Social Research?

"Researchers try to reduce sampling errors". Well Jesus, hopefully.

Also, I would not have guessed that "Periodic probes" are follow-up questions by interviewers. A neutral request to clarify an ambiguous answer? Sounds more like a forceful interview method.