how google mobile index which rolls out today can penalise your shopping website

Google is updating its mobile search index to crawl mobile websites to determine their content relevancy in search results, the search giant announced on its official Webmaster blog last week. Google still looks at the desktop versions of the page to evaluate its relevancy to the user on smartphone search results, the search engine says. This is a problem if the mobile site has less content on it than a desktop siteGoogle basically treated your mobile page as an alternate version of the same content, “The problem is, when shoppers search for a certain product feature or keywords and click on your mobile page from Google but can't find that phrase on the page, they get frustrated at Google for showing irrelevant listings.” This change will impact e-retailers that have a separate mobile site, often referred to as an “m.” site, which is 142 retailers of the 500 merchants ranked in the Internet Retailer 2017 Mobile 500 according to Top500Guide.com. 
Retailers that use responsive design or dynamic serving (another form of responsive design also referred to as hybrid or adaptive design) shouldn’t have to make any changes, Google says. 357 e-retailers use a form of a responsive design in the Mobile 500. 

 So what will this change ?.Although Google wants you to have a mobile site,even if you dont, it will crawl your desktop version instead. Google said, “If you only have a desktop site, we’ll continue to index your desktop site just fine, even if we’re using a mobile user agent to view your site.”However in case you have a mobile site, you need to ensure the" copy ,images and links are similar enough to the desktop version so that Google can consume the proper content and rank your site as well as it did by crawling your desktop site.

Retailers that do have a separate mobile site should use the Google-recommended mobile search engine optimization mark up in its code,according to google mobile best practices guidelines