Attempted to buy two items, they charged me five times. When trying to get reimbursed their answer was basically "tough luck, we aren't the seller so we can't do nothing about it, okay bye. Then the seller tried to convince me to change my reviews and started to be reallllly insisting. It's called reviews for a reason.
The worst part is that G2A never cared they charged me five times, no matter how much I told them. So I guess they allow such practices cause they didn't seem to mind at all that one of their sellers was a scammer.
All of the horror stories you hear are true.