Will it make any difference to SEO on an ecommerce site if they use their SSL certificate (https) across every page

[Sayers]

I know that e-commerce sites usually have SSL certificates on their payment pages. A site I have come across is using has the https: prefix to every page on their site.

I'm just wondering if this will make any difference to the site in the eyes of Search Engines, and whether it could effect the rankings of the site?

[Chris.Menke]

Nicola,

According to John Mueller from Google Switzerland,  HTTPS-only sites are fine and  there’s absolutely no need to shy away from them so long as they're  implemented properly. There’s certainly no penalty involved with running your site on HTTPS-only when done right.

https://plus.google.com/106413090159067280619/posts/ZZVAS65mmw4

[matbennett]

As Chris says, this shouldn't be a problem at all. We've done this on a few stores and not seen any measurable impact in either direction from it.

The only thing to be aware of is the possibility of introducing canonical URLs. http://example.com and https://example.com are different URLs. If both are accessible and return a valid header then both can be indexed.  Always worth ensuring that you either have a redirect, a rel=canonical or robots.txt addressing that issue if you have https in place.