Only Marketplace listings that are distributed as a free download could have the Sitefinity Validated logo on them. All Sitefinity validated marketplace listings are hosted by Telerik. The Sitefinity Team has tested those extensions against a blank Sitefinity project in order to ensure that they do not break the system. Extensions are tested on the respective Sitefinity versions that they support. All downloadable files have also been vetted for malicious software. It is the publisher’s responsibility to ensure that their Sitefinity extensions do not have bugs and work as stated on their description.
Note that even though a Sitefinity extension has been tested on a blank Sitefinity project, Telerik cannot be held responsible, if an extension breaks a Sitefinity website due to customizations that have been made to it.