If you are looking for a technical solution you might want to check out..ahem... my company ThreatMetrix.
As ex paypal Im guessing you have invested a lot in risk management, ML and automation etc as its really technically difficult to make such a broken process like online payments this simple so you may have it all covered.
What we can bring to the table is a (300ms) https name value pair API that delivers aggregated intelligence in real-time based on transactions, identities, devices and behavior across 6000 sites that represent over 1MM individual CNP txns on a daily basis (only 1/5 of Paypals txns but hey we are a startup!) which you can ingest into your rules engine or risk models during, before or after the payments authorization/capture.
We dont just provide a score which can be impossible to integrate with other ML engines we also provide customizable (by you) reason codes/triggers that can be used to characterize behavior e.g. customer's computer associated with 3 difference identities and 4 different proxy ip addresses across global network in last hour....Data Geeks geek out on it as we also provide full attribute data back in the API response so provides a good way to do feature extractions for SVMs etc. We have been proven to reduce FP and increase TP.
We currently process peak 700 tps with about 20% degradation in performance at load. We suck at batch processing cause its just not our thing. I head up products and one of the founders so not selling just helping as I think you have a solid offering that should do very well.
Paypal bought Fraud Sciences for 170M but you can rent ThreatMetrix ;-)