As a person who enjoys going out and harassing people with questions about their faith (yeah, I'm one of those guys) you either have to become really good at debating people who know what they're talking about, or you lose the debate.
I have a lot of little tricks I've picked up in my time debating people, and there's one question you can ask a religious person that really shakes up the conversation. When you ask it, they have no choice but to pause and rack their brain because you've just posed a perfectly reasonable question, which is not some sort of deception and forces introspection. As an added bonus, if there are any people listening in on the conversation, they can always tell that the person you've asked the question to has had the ground beneath their feet shaken a little.
All you have to do is riddle them this - If there was no God, would you want to know?
If they ask for a way that you could do this I usually say something like, if we found another dead sea scroll and on it was a passage that said "by the way, this is all crap" or something like that.
Now, this either goes one of two ways. Either they admit that if there was no God, and they could have a definitive answer, they would want to know. At this point a huuge door opens up where you can talk about reasonable evidence and the history of religion. Really if it comes down to that, you've won the debate because you've done the impossible and gotten a religious person to listen to reason.
Its not always so cut and dry though, sometimes they admit they would want to know then close right back up, but this doesn't happen very often in my experience.
The other possibility is usually much funnier because you get to watch them squirm and the audience immediately turns over to your side.
The other option is for the to say that they wouldn't want to know if there was no God. Like, how close minded is that? I have definitive proof that your deity doesn't exist and you wont listen?
They try all sorts of tactics here such as "it would always be false evidence" or "God is bigger than evidence" or other room-clearing nonsense such as that. Really the conversation is over at this point too, because how do you reason with someone who rejects reason?
Anyways, I hope this helps all yall people the next time you're having a religious discussion. If it works out for you, give me a comment, I'd be happy to hear about it!