The primary function of the passage as a whole is to
evaluate the utility of a practice
The passage describes a marketing strategy practiced by some professional service firms, outlines the arguments in favor of its use, and then describes the drawbacks associated with the strategy.
The popularity of the practice is not discussed in the passage. The passage does not include a demonstration of how to institute unconditional guarantees. The ethical issues are not addressed by the author. In the first paragraph, the author does give reasons for why firms pursue the strategy, but that is not the purpose of the passage as a whole.