The issue which Paul is clearly defending himself against here is that he did not receive any support from the Corinthian church at all: when he needed financial support it was the Philippian church who provided it. So, why accept gifts from one church and not another? Well, the reason was a practical one: he only accepted financial support from a church once he had moved on from that place. While he was living in Corinth or Philippi he had to be under obligation to no one; it was a wise decision so that he could maintain his independence.
So, why were some in the church at Corinth annoyed about his refusal to refuse their largesse whilst staying in that city? Firstly, because working with your hands- he would have been tent-making as well as preaching- was considered to be beneath a person like Paul, who had such great gifts or oratory and apologetics. Secondly, teachers were meant to make money from talking and this was an age when an enormous amount of money could be made: The Roman Emperor, Augustus, hired Verrius Flaccus for the modern day equivalent of a quarter of a million pounds a year!
The incongruous thing was that the false apostles took money from the Corinthian believers and then used the fact that Paul would receive no money to demonstrate that they were the real apostles and that Paul was a fake! They reckoned that Paul refused to take anything, because his teaching was not worth anything! Paul accused them of Satanic activity, because by their actions they were harming the church and discouraging others from joining. Here are four tests by which we might know whether someone else or ourselves are truly Christians:
1. Do you know salvation through the cross of Christ?
2. Are you growing in the power of the Spirit?
3. Do you or they have a great desire to spread the Kingdom of God by example and by preaching and teaching?
4. Are you or they bringing others to Christ?
Let us test ourselves!