Guaranteed Payments for Sellers
The Bad:
Poor integration. Users are often confused how to interact with the originating ecommerce site since they never login to that site in most cases and emails are communicated anonymously for many customers.
100% email driven communications. If someone initiates a chargeback and you miss the email that says you have 24 hours to respond you're SOL. They send out so many automated messages for whatever reason its hard to discern what is legit/true and not just a glitch of their systems.
And like others have said, the shipping integration is absolutely horrendous. Having the timeout default to checkout conditions in 75% of the orders stinks