ok, as someone who actually HAS used kaplan's higher score guarantee (to retake the course, not to get a refund), i'll speak from experience.
i took the kaplan online course last summer in prep for last august's test. i didn't anticipate having to take the test twice, but just to make sure, i did everything that the online course listed as REQUIRED. i took the test and was not happy with my score (only 4 points higher than my diagnostic). i called kaplan the next day (i think it was Oct. 15, a little less than 2 months after the august test). they had to go through my course sylabus to make sure everything was completed. the only thing that wasn't completed in their system was FL 5. they told me i wasn't eligible for the HSG b/c i hadn't completed that assignment. i told them i had completed it, but that it was so close to the exam that i didn't want to waste time putting my scores in their system and i just scored it myself. they had to check with the manager, and once they got the ok, they re-enrolled me in the course.
moral of the story: the higher score guarantee can be used if you meet all the eligibility criteria. just make sure to do all the required assignments.