Can I run multiple stores with one Cart66 account?
No, each store needs to have it's own Cart66 Cloud account. The issue is not a permission or licensing problem. The issue is that the Cart66 service is designed to run a single site. Here are some examples as to why that is.
The secure checkout page
Cart66 Cloud provides a secure hosted checkout page which makes your store PCI compliant without you having to worry with SSL certificates or anything else. The secure checkout page is skinned with your WordPress theme so that it looks exactly like the rest of your WordPress site. Of course, you can only skin your secure checkout page with one theme. If you had multiple sites using the same Cart66 account they would all use the same secure checkout page, but you could only use one of your sites to skin the secure page. Therefore the checkout page would not look like the other 2 sites.
Cart66 Cloud provides you with a secure custom subdomain to host your secure checkout page. Each Cart66 account comes with one custom subdomain. If you were using the same account on multiple sites all the sites would have to use the same subdomain and the same checkout page.
The receipt page redirect
After a successful sale, Cart66 redirects your customer back to your WordPress site to view the receipt. The Cart66 settings specify the location of your site. If you were using the same Cart66 account for multiple sites all of your customers, no matter which site they were shopping on, would be redirected back to the same site to view their receipts.
Amazon cloud storage
Each cart66 account comes with free Amazon S3 storage to securely host and deliver your digital products. If you used the same Cart66 account on multiple stores, all the digital products for each store would be dropped into the same secure storage bucket and available to each of the stores.
All of this is to say, the limitation of one Cart66 account per store is not a licensing issue, it is a technical issue having to do with how the Cart66 service works.