Nothing can be 100% verified in war.
But you can use deductive reasoning to come to a logical conclusion.
Russia say it's only targeting "military or operational targets"
So why are cities and town over 50km away from any military instalments being shelled, you can't divert a artillery shell by 50km. It gets loaded in to the barrel, shot out and droped no more than about 22km away from this target. And the constant artillery bombardment we have seen on some cities and towns of cluster bombardment it's impossible.
Now the other thought of dress up. Why would 100,000 Ukrainians play dress up and sit in Russia/Belarus for weeks before invading their own country in Russian marked vehicles? Do you think Russia and Belarus would allow this...I don't think so. We've been able to track by satellite images the advance of some convoys and they clearly came from Russia.