How can anyone who hasn't realised the truth, claim that Mahatma Buddha or any other person in history realised God or the Truth? Isn't it possible that whatever they have realised is just a psychological effect? Doing continuously hard practices leads to affect their mind and they tend to believe that, yes, this is the truth. They started lying to themselves that they know the truth?
I truly respect their teachings which shows us the path to live a good life. I am just talking about the real truth (if there is any).

With love.
The truth of the Buddha is the method to end suffering. When a person tests the method &amp; it works, they know the truth of the method, similar to when medicine is effective in curing in a sickness. 

In Buddhism, there is no truth apart from personal verification, as taught: 


  "Knowing thus and seeing thus, would you say, 'The Teacher is our respected mentor. We speak thus out of respect for the Teacher'?"
  
  "No, lord."
  
  "Knowing thus and seeing thus, would you say, 'The Contemplative says this. We speak thus in line with the Contemplative's words'?"
  
  "No, lord."
  
  "Knowing thus and seeing thus, would you dedicate yourselves to another teacher?"
  
  "No, lord."
  
  "Knowing thus and seeing thus, would you return to the observances,
  grand ceremonies, &amp; auspicious rites of common contemplatives &amp;
  brahmans as having any essence?"
  
  "No, lord."
  
  "Is it the case that you speak simply in line with what you have known, seen, &amp; understood for yourselves?"
  
  "Yes, lord."
  
  "Good, monks. You have been guided by me in this Dhamma which is to be seen here &amp; now, timeless, inviting verification, pertinent, to be
  realized by the observant for themselves. For it has been said, 'This
  Dhamma is to be seen here &amp; now, timeless, inviting verification,
  pertinent, to be by the observant for themselves,' and it was in
  reference to this that it was said.
  
  Mahatanhasankhaya Sutta