Shaikh Saleh ibn Fawzaan ibn Abdullaah al Fawzaan says:It is a must to know what the condition for the caller are, so that the call continues upon a correct methodology, and so that differences do not occur between the callers to Allaah. Differing will happen due to ignorance, but if the callers gain good understanding in the call to Allaah and they know the correct methodology, they will never differ. Differences only ever occur when people who are unqualified enter into the Dawah, and so whoever is not equipped for it with beneficial knowledge and sincerity to Allaah, the Most High, then differences will occur. However, if the callers gain a good understanding in the call and their intentions are purely for Allaah, the Most High, and their objective becomes (seeking) the Face of Allaah, they will never differ. Rather they will help each other and they will be one hand. They will cooperate with righteousness and piety.