A problem one encounters while trying to do good, such as giving to a fraudulent charity, shouldn't cause a Christian to become discouraged from doing good.
Good charity depicted above.
Some might decide not to give to a charity again while others might first ask if there weren't still many good ones to give to.
In trying to lead a Christian life, there will be times when a problem occurs, but this shouldn't discourage a Christian from trying to do good. Consider giving to a charity only to discover it was fraudulent. Some might decide not to give to a charity again while others might first ask if there weren't still many good ones to give to.
A problem that results from something someone does doesn't necessarily mean that what is being done is wrong. Even if a charity is discovered to be fraudulent, does that mean there aren't still good charities and people who need monetary support, for example? The general idea holds true for helping teach people from the public about Jesus, which involves both problems and beautiful outcomes.
It is already taught in the Bible that people who decide to become Christians will face difficulties, but it is not until some of those difficulties are encountered that a Christian may really realize what that means. What helps is realizing when the good aimed for is still good and can still be achieved even after an unpleasant experience has been encountered. Trying to help people in need is not an idea to be given up on after putting one's money in the wrong hands, for example.