In the Bible (New International Version), Matthew 7:17-20 states:
17 Likewise, every good tree bears good fruit, but a bad tree bears bad fruit. 18 A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. 19 Every tree that does not bear good fruit is cut down and thrown into the fire. 20 Thus, by their fruit you will recognize them.
In the United States, the term “Fruit of the Poisonous Tree” is a legal metaphor used to describe evidence gathered with the aid of information that was itself obtained illegally. The reasoning being, if the source of the evidence (the "tree") is tainted, then anything gained from it (the "fruit") would also be tainted. This “Fruit of the Poisonous Tree” doctrine stems from the 1920 case of Silverthorne Lumber Co. v. United States.
Evidence gathered under the “Fruit of the Poisonous Tree” doctrine is not generally admissible in court. An example of evidence gathered in this manner, if a police officer conducted an unconstitutional, warrantless search of a home and obtained a key to a gym locker, in which was found illegal drugs; the drugs would probably be excluded from evidence in accordance with the fruit of the poisonous tree doctrine since the it would not have been found without the finding of the key, which was found illegally.
We could also apply the “Fruit of the Poisonous Tree” doctrine to bogus martial artists. If a grandmaster of a martial art is found to be bogus, the every rank awarded by the master is bogus, and every rank awarded by these people is also bogus, etc. Whether you like it or not, whether you agree with it or not, and regardless of whether it is fair or not, any rank that stems from a bogus linage is tainted and is also bogus. You may not have been aware of the fraud being perpetrated against you and you may have had the most honorable of intentions when obtaining the rank, but the rank is still bogus. When you buy what you legitimately thought was a Rolex watch, and it turns out to be a fake, the fact that you were scammed does not make the watch real—it is still a fake.
Be careful when dealing with martial art instructors, masters, grandmasters, schools, and organizations. After you have invested all your time and money in them, you may find they are bogus. It is a shame that you were conned, but that does not suddenly make your rank legitimate. If you have been a victim of a scam—leave—and start over again at a legitimate school. The basic skills you have learned will still be with you, so it will be easier to progress in the ranks of the new school.