Regarding the question, ‘Should the devotee always speak the truth to everyone in all circumstances?’. The answer is yes, one should always speak the truth, but qualified devotee will be able to speak the truth always very palatable to everyone so that it will sound pleasing even to his enemy, that is the art of speaking truth. It is certainly so that we must speak the truth to all people, but how you say it that is another thing: satyam bruyat, priyam briya. When you become yourself little more experienced in Krishna Consciousness by preaching work and if you are sincere and serious to make progress in spiritual understanding, you need not have to worry yourself further because the truth will always be spoken by you in the proper manner. Krishna will give you that intelligence, you need not be concerned for it. Simply try to please Him always by your sincere service and chanting, that’s all. Of course, for doing business with businessmen you have to lie business. Just like Krishna Himself, the Supreme Personality of Godhead, sometimes He also had to also fabricate something in emergency situations. Although He made promise not to interfere in the Battle of Kuruksetra, He was forced to break His promise just to save His pure devotee. So there is no prohibition one shall never tell lie, because for business of carrying our propaganda work sometimes it may be necessary. Krishna Consciousness means practical living, not something utopian or idealistic and vague. We simply do the needful, whatever pleases Krishna most, that’s all. Gradually you will understand what it means to please Krishna and what it means to displease Krishna. That you will learn by studying our books and by yourself engaging in practical devotional service. In the material dealings there is always there is always something undesirable, but even so you cannot give up your occupation. Just like fire is very pure, still there is some smoke. You cannot avoid it. All these things can be rectified when the result is offered to Krishna. Otherwise even though you may do very honest business it has no utility whatsoever.
Ref >> Srila Prabhupada Vani.