The basic difference between CISSP sample test questions and those from the real CISSP exam is that with the former you get questions that were based on previous exams but are not exactly like those on the previous exams. The difficulty with the latter is that it is actually illegal to use real questions from actual CISSP exams. Thus, if you are a company that intends to serve people by offering a CISSP sample test, it is never a good idea to rip off questions from actually CISSP exams because you can get charged (and maybe convicted) for stealing trade secrets.
An ideal CISSP sample test is one that has been made up from scratch by the website staff yet still relies on the principles and concepts the applicants will encounter in the Common Body of Knowledge or CBK database. It should be able to challenge the student with the CISSP sample test questions but not use any real questions from real exams.
So where is the harm in using questions from past exams? The harm is that those exam questions and the exams themselves are considered copyright secure. This means you the user have the responsibility to report anyone who has been using real exam questions for the CISSP sample test and making money off them. If not, it will be up to law enforcers to pursue the case.
A good example of someone who was successfully convicted of using real exam questions as the piracy of trade secrets is Robert Keppel. Keppel earned huge profits from the sale of trade secrets a.k.a. exam questions from his www.cheatsheets.com website and paid very dearly for his actions eventually. So when trying to study for the CISSP exam, use original questions from original CISSP sample test makers.