2 Corinthians 11:7
Have I committed an offence in abasing myself that ye might be exalted, because I have preached to you the gospel of God freely?
Note 12 at 2Co 11:7: Paul was asking if he had sinned by preaching the Gospel free of charge to the Corinthians. He humbled himself by making tents to support himself and his companions in ministry (1Co 4:12, 1Th 2:9, and 2Th 3:8). While other religious teachers and philosophers demanded payment for their services, Paul showed unselfish service toward those to whom he ministered.
Paul was pointing out the irony of these accusations against him. How could people receive an evil report against someone who had served them so selflessly? His actions should have spoken for themselves. In 2Co 11:12, Paul said the reason he had done this was to stop false apostles. How could those who were charging for their services impugn those who gave everything they had freely? Yet, this was the situation Paul found himself in.