2016 is the year for SSL everything.  This year Google will change it’s ranking system to favour sites that are secured with a SSL certificate. And from September they will stop indexing e-commerce checkouts that do not have a SSL certificate.  Yes, that includes your marketplace.

As part of your Marketplace setup you should include purchasing a SSL certificate for your domain. Ideally one with 3 years of more life, and from a trusted provider.

https://www.digicert.com/welcome/ssl-plus.htm