On Brandon Vogt's excellent Strange Notions, Dr. Kreeft presents the Common Consent Argument for God. This is what he's elsewhere described as a "probable proof". Put simply, the vast majority of people throughout time and over the earth have believed in an almighty being. Is it more likely that God exists or that the vast majority of people have been wrong about a very important aspect of their lives?
Does this argument prove that God exists? No.
What does it do, then? It makes explicit one of the costs of atheism. To believe there is no God, you must also believe that the vast majority of people throughout history have been wrong about something so important.
One may try to explain away historical belief in God. The people didn't know any better. They were less intelligent or less educated. They were forced into belief or blind to alternatives. They didn't have modern science to fill in the gaps in their knowledge. Charlatans pulled tricks on simpler people and fooled them into believing.
In these cases, I'm reminded of some debunking shows, like Fact or Faked, that attempt to prove something didn't happen by showing how it could be faked. There's a problem with that approach. Proving that something can be faked doesn't prove that it always is faked. There was fake vanilla in the cocoa I drank this morning; that doesn't prove that real vanilla doesn't exist.
Imagine that I see a black cat in a tree, and later you see a cat-sized black plastic bag blowing around in the same tree. What does that tell us? It tells us very little. I may have mistaken a bag blowing in the breeze for a cat, or I may have seen a real cat. The second viewing provides an alternative explanation but not an ironclad argument.
Likewise, there are some who seek to disprove spiritual experiences or miracles by demonstrating how they can be triggered or faked. While I believe there are fake spiritual experiences and fake miracles, the possibility of fakery doesn't disprove specific cases. The possibility of people believing in God for poor reasons -- out of ignorance, for example -- doesn't affect whether or not God actually exists.