1) how easy is service to cancel. Put your cancellation link online not behind a business hours automated phone tree.

2) how trial periods work. Send customer email 3 days in advance to notify them that billing will begin if they don't take action and amount of bill with an easy way to cancel if desired.

Some SAAS I think is always high risk, SEO tools, email marketing, adult services related etc? Someone probably has a better high risk SAAS list. Basically, can someone uses a stolen card, or even their own card and signup for this service, spend $10K blasting emails to people, then claim unauthorized?