What does 2 Corinthians 12:18 mean?

False apostles in Corinth had started a campaign against Paul, challenging his status as a true apostle. Their true goal was probably to get money from the Corinthians, as well as leading them to believe in a false version of the gospel of Jesus.

One of the accusations they may have used to turn the Corinthians against Paul was that he was planning to take some of the contribution they were making to the Christians in Jerusalem for himself (2 Corinthians 8:10–21). They may have felt the need to do this because Paul refused any payment for himself at all from the Corinthians (1 Corinthians 9:11–12; 2 Corinthians 11:7–12). Meanwhile, the false teachers gladly took money. Perhaps the deceivers also wanted to keep the Corinthians from donating to the Jerusalem Christians, so they'd have that much more money for themselves.

In any case, Paul is asking the Corinthians to really think about the charge. Do they have any evidence, at all, that Paul or Titus was cheating them? Paul specifically sent Titus and another man to them. Did Titus take advantage of them in any way? Wasn't he just like Paul in refusing to take funds from them? Paul wants the Corinthians to see for themselves that the charge is not supported by any facts.