Here's another site checker for those that are using Magento's shopping cart software. Unfortunately, there's no easy way to determine if a site is using it or not without digging into the source code for the page. However, if you run a site through Magereport and it's not using Magento, it'll tell you.
http://magereport.com
Medium risks or Unknowns (depending on what the issue is) are most likely OK. High risks displayed should be a red flag.
I should also add that Magento is wildly popular with a lot of e-commerce sites in China. And unfortunately, many of those sites are extremely vulnerable as they rarely update the shopping cart software.