Determine if there actually has been fraud or misrepresentation
Fraud defined as "false representation of material fact made with knowledge of its falsity and with intent to deceive the other person. The representation must be believed and acted upon by the party deceived to his disadvantage. Fraud may involve the making of a statement that reasonably would have the effect of discouraging an avenue of inquiry into the true facts. Misrepresentation requires an affirmative act taken by the alien, including an oral statement in an interview or by submitting evidence containing false information.
Determine if and how the government has made a factual or legal mistake
The USCIS makes different kinds of fraud findings- document fraud, fraud or misrepresentation to obtain a visa, entry to the U.S. or other immigration benefit, marriage fraud (sham marriage) and others. There are many ways that the government can wrongly determine that there has been fraud or misrepresentation. It may wrongly attribute the fraud of a 3rd party to a person who was unaware of the fraud. The government may also fail to determine if a misrepresentation was "material." The government may also have misunderstood the facts of a case, overlooked evidence, or failed to properly weigh the evidence presented. It is also important to recognize that the government should have substantial and probative evidence to support its charge of fraud.
Responding to a charge of fraud or misrepresentation
(1) Assess the charge and, if wrong, challenge it; (2) file a Freedom of Information Act request and insist on inspecting the record to get at the information the government has; (3) If the charge is correct, don't deny or avoid it, rather, admit it and assess whether there is a waiver of inadmissibility available and the chances of success; (4) a marriage fraud charge is different and can be unwaivable in many situations- this should be rebutted with clear and convincing evidence of a good faith marriage.
Seek administrative or judicial review
Certain fraud determinations can be reviewed in removal proceedings. A denial of an I-130 petition can be appealed to the Board of Immigration Appeals. A denial of an I-601 waiver can be appealed to the USCIS Administrative Appeals Office or in removal proceedings in front of an immigration judge. Assistance of an experienced immigration attorney is likely essential in such a case.