How do we know the casualty numbers are legitimate?

[DefendIsrael]

I, like most people, want as little innocent people to die.

However, from my understanding, the death toll of civilians in Gaza comes from Gaza officials...and Gaza's government is HAMAS, the same organization that wants the destruction of Israel, and has been shown to lie to appeal to the western world. For example, the picture on twitter by Hamas that really was from Syria. or the BBC clip of the injured man that was shown to be fine seconds later. If they're lying about this, couldn't they easily be lying about the casualty numbers too?