To ensure that Google can process your feed, please use an XML schema validator to ensure that your feed complies with the requirements of the schema before submitting your feed to Google. Google will also verify that your feed complies with the schema before accepting your feed.
There are a number of tools available to help you validate the structure of your XML feed. One such tool is xmllint from www.xmlsoft.org.
You can use xmllint to validate your feed with this command:
xmllint --schema http://www.gstatic.com/productsearch/static/reviews/5.0/merchant_reviews.xsd --noout file.xml