It is vital for da'wah carriers to be honest and transparent. It is common for Western politicians to always give an answer even when they don't have the knowledge of an issue. The da'wah carriers should ensure they do not become like them who aim to protect their position and status amongst others by giving answers without understanding the ahkam and evidences about issues.
For example someone may be asked, "Is it permitted to be a councillor in the local government in Dar al-Kufr?" They may answer, "It is permitted as its reality is different to an Member of Parliament." This would be a disaster for the da'wah as the person would have permitted something haram without having knowledge of the shariah rule. He would be sinful for doing that and would be guilty of misguiding others.
Another example may be someone is asked, "Is it permitted to send your children (non baligh)to schools which teach Kufr?" They may answer, "It is permitted as long as you refute it to them when they come home and attempt to build the Islamic concepts in them." Again this would be a grave error as the person would have permitted something haram and it would allow childrens minds to be filled with the Kufr culture in a stage when their minds are not developed enough to distinguish between right and wrong.
In order to build the Islamic values and the adherence to the ahkam shariah within the Muslims, da'wah carriers need to ensure that they have knowledge of the ahkam shariah so they can work to propogate them accurately and not misguide Muslims in the name of Islam.
‘Umar (ra) said: “We have been forbidden from pretence (of knowledge).” [Reported by al-Bukhari]
Masruq said: We came upon 'Abdullah bin Mas'ud (ra) and he said: "O people! If somebody knows something, he can say it, but if he does not know it, he should say, 'Allah knows better,' for it is a sign of having knowledge to say about something, which one does not know, 'Allah knows better.” Allah said to His Prophet: “Say (O Muhammad SAW): "No wage do I ask of you for this (the Qur'an), nor am I one of the Mutakallifun (those who pretend and fabricate things which do not exist).” [TMQ Saad38:86] [Agreed upon]
The Imam of Darul-hijrah; Malik b. Anas (rh) was asked 40 questions. Regarding 36 questions he said: I don’t know.
If we don't know the answer to a question we should simply say, "I don't know" and then find out from someone who is a trusted Faqih or person of knowledge.