Some comments on that in this thread:
https://news.ycombinator.com/item?id=16216682
https://news.ycombinator.com/item?id=16216936
We vet our merchants before onboarding and make sure to work with high-integrity companies. We monitor orders not just for identity fraud, but for merchant / collusion fraud.
That being said, we can certainly make mistakes. We also end up in the red some months with some clients. The good thing is that when we make a mistake, we pay the cost, not the merchant (which is contrary to the current state of the industry).
We have made reasonable profit per client even with our costs, but the real winners are our clients driving millions in newfound revenue.