Adam Clarke on 2 Corinthians 11:12

But what I do, etc. - I act thus that I may cut off occasion of glorying, boasting, or calumniating from them - the false prophets and his partisans, who seek occasion - who would be glad that I should become chargeable to you, that it might in some sort vindicate them who exact much from you; for they bring you into bondage, and devour you, 2Cor 11:20.

Nothing could mortify these persons more than to find that the apostle did take nothing, and was resolved to take nothing; while they were fleecing the people. It is certain that the passage is not to be understood as though the false apostles took nothing from the people, to whatever disinterestedness they might pretend, for the apostle is positive on the contrary; and he was determined to act so that his example should not authorize these deceivers, who had nothing but their self-interest in view, to exact contribution from the people; so that if they continued to boast, they must be bound even as the apostle, taking nothing for their labors; which could never comport with their views of gain and secular profit.