Go check out their forum, you will see several request for help by paying customers unanswered. When I see this kind of thing happening, I stay away. There are many well built plugins that have been abandoned and still reside on the WP plugin repository. This does degrade WP by degrees.
A shop application is extremely critical to any business and when support is needed, it better be there.
I think the WP staff, should create policy that if developers want their plugin on the WP site, they need maintain business some level of business ethics. If those at Webstore Cart need to ask more for their product to maintain customer service, then they need to do that.