Being the innovator, PayPal grew up with these fraudsters, building an in-house database of knowledge about how to handle them as they cropped up one by one.
If you're talking about building a PayPal competitor at this point, you're launching at a point when there isn't going to be as much investor interest in your startup combined with a mature fraud ecosystem prepared to shut it down.
And those are only the problems we know of.
I think credit checks are overrated, as far as fraud mitigation. The relative risk profile would need to be determined. That said, OpenCamp represents a relatively low risk to PayPal in real terms. They have the event booked with the Hotel, They have real organizer profiles.