Opinion Stage offers the option to white label all your items including quizzes by removing the Opinion Stage branding from the interface (and optionally adding your own logo). However due to a Facebook limitation we are not able to remove the opinionstage.com label from Facebook shares done from quizzes.
To determine what to share Facebook scans the shared URL and retrieves from it the title, description & image. Because we want Facebook to retrieve the quiz title, quiz description & quiz image we need to hand Facebook the Opinion Stage iframe URL (as opposed to the URL of the site hosting the quiz).
This causes Facebook to put the OpinionStage.com site indication on the share without allowing us to change it. It's important to note that clicking the share will go back to your site (since we can override the link) so you don't have to be worried about that.
No other quiz service we are aware of was able to overcome this small branding issue, and we weren't able to get Facebook to change their policy on the matter either.
The good news is that from our research, it has no affect on the click rate and you can always add your branding in the messaging/images of the share and on the quiz itself.