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Hello All, Have you guys seen any positive increases in search traffic since you have implemented this schema to get the search bar within the search results?

Just sounds like a strange anomaly. "Sell my car" is a very broad search term. With the constantly changing landscape of the Google SERP's, it could well have been something like a new video result that was a video on selling cars that pushed you off the page. Private browsing also blocks cookies and that's not a consistent way to monitor results.

I'm assuming you'd like to have 5 star ratings for the product? Can you go back to those people who gave you a testimonial and get them to give you a rating out of 5? If so then great, but if not perhaps you can judge each review fairly and come up with a star rating. Once you've done this you can use Schema.org (try the Schema Creator if you're not sure how) or hReview to try and get some rich snippets showing. Use the Rich Snippets Testing Tool or Bing Webmaster Tools to validate.