Unfortunately in the US once the government has issued permanent residence (not conditional) to someone it is highly unlikely that even if evidence is presented after the fact that the marriage was a "sham" will they do a revocation of the permanent residence. Marriage fraud after the fact is pretty low on the totem pole so to speak for them. I too have known people to stay married long enough to obtain permanent residence status. Immigration in the US is not how do you say, very consistent. What one gets away with another one won't. Anna is right on the mark, a true scammer will do whatever is needed to scam the system and possibly (more than likely) the person they married.
