No offense, but one of the qualities of any standardized test is its ability to be repeated in order to ensure accuracy. Thus, people who are certified to give IQ tests, REAL IQ tests (such as the Stanford-Binet), are given a script from which they cannot deviate while administering the test. This consistency is what allows IQ scores to be compared, because it ensures that each subject has had virtually the same test taking experience.
I don't know where you got your information, but any legitimate IQ test, meaning the kind you take with a real psychologist in a professional setting and NOT on the internet, is completely and absolutely comparable to the scores of all other test takers. Any other test is simply not an official or credible IQ test, and thus should not be taken into consideration.