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Hello Sarmad, I don't recommend having a single-page website on the front-end. You can handle the loading of content however you like: Javascript, lazy loading, dynamic serving.. as long as each section/page has a different URL. A hashtag is not a new URL, but rather a named anchor link to somewhere else on the same page. Thus, using this technique you would only have a single page indexed in Google, not a lot of room to target different topics. Lots of sites use the parallax design style, but have multiple pages. Parallax and single-page are not necessarily synonymous. The most common use on a multi-page site would be to tell a story on a landing page or the home page. More concerning to me right now is that it looks like they're putting their clients' sites on their own subdomains, which are fully indexable by Google: https://goo.gl/z9dSDl .

Good point Eric! But the number AND quality of links still matter - even if it isn't called PageRank. Just clarifying that link authority and relevancy is being passed from one site to another...