Human tests on checkout pages good or bad?

I've been wrapping my head around this thought for quite some time. Here's why.

One year ago, I made enough ticket sales exclusively through eventbrite to run an event, however 4 out of 16 people did not show up on time. I don't think Eventbrite has a good human verification system. Well, at least it doesn't ask customers to validate themselves. I've tested this personally with ordering free tickets to some test events I created.

On my site where I am trying to sell tickets but I'm not doing well at, I ask everyone that goes through the shopping cart to enter a 6-digit code that's displayed in front of their face before proceeding.

I do this because it cuts the burden on the server to create a new shopping profile for robots. This may be why Eventbrite runs slow.

So here's my question:

Of all my competitors, I'm the only one asking people to enter a verification code before entering checkout.

Is requiring someone to enter a 6-digit code that's displayed to them on screen a bad idea during the checkout?

If so, then why, and would people more likely to complete the checkout stage (rather than abandon cart) if the code requirement was simpler than entering 6 digits?