The Apostles Peter and Paul had a similar problem. They would win Gentiles to Christ, and then someone back home would say that they were doing the wrong thing. Eventually, the Christians had to hold a council at Jerusalem to decide the issue. But what gave the critics the authority to evaluate two men who were getting large numbers of people saved?
A major problem with missionaries today is that they have to answer to a board that has no Scriptural authority to evaluate them. Missionaries are forbidden to participate in evangelistic outreach with other groups on the field. They are also forbidden to do anything that might offend the organizations and churches that provide financial support for the board.
I'll be talking about this one for a while.