Our fraud detection software, SiftScience, works continuously in the background to blacklist members who exhibit behavior attributed to spammers and scammers. We also monitor our listings daily and follow up with all customer support messages within a few hours.
We use Stripe.com as our payment processor and they are one of the best and most secure around. They power payments for thousands of small and large companies including Twitter, Kickstarter, TaskRabbit, Lyft, Shopify and more. They are certified PCI Level 1, which is the most stringent level of compliance.