1. Subpoena power.
In court, plaintiffs and defendants have subpoena power, which is the ability to require someone to testify or produce information in a lawsuit. If you fail to comply with a subpoena, you can be held in contempt and placed in jail. If you are served with a subpoena but consider it an improper request, you can move to quash it. You must file a motion to quash and set the matter for hearing before the date specified in the subpoena. You can try this by yourself, but it is unlikely to be successful without an attorney's help.
A subpoena can be quashed when it seeks privileged information or protected matter; fails to allow a reasonable time to comply; requires excessive travel to comply; or otherwise imposes an undue burden on the party subject to it. The NCAA has no subpoena power. Accordingly, it has no way to force a party to divulge information.
In court and in NCAA investigations, there is a duty to speak truthfully. If you do not in court, you can be charged with perjury. If you do not in an NCAA investigation, you can lose your eligibility if a player, or issued a show-cause order if a coach or administrator. If you do not speak to the NCAA at all when information is requested, you will likely be penalized to a similar extent than if you had lied to the NCAA. Accordingly, you should speak to the NCAA when requested, even if you are not obligated to do so.
2. Legal standards.
As discussed elsewhere, there are no legal standards in enforcing NCAA rules. A criminal defendant must be proven guilty beyond a reasonable doubt. A civil plaintiff generally must prove his or her case by a preponderance of the evidence. Sometimes, the standard is "clear and convincing." Without legal standards for determining guilt of a party, it is exceedingly difficult for the NCAA to find a school or involved individual guilty, because the school or individual can simply claim there is insufficient evidence.