by Ann Smarty
Google is consistently moving from being a search engine to being a publisher and a tool. Their knowledge graph, quick-answer boxes and price-and-service comparison tools are slowly removing the need to ever click the publisher's (service provider's) link.
The truth is, the core of the algorithm has remained the same: It still heavily relies on backlinks. The minor things have changed: The algorithm is harder to manipulate; it has become smarter at recognizing authority and it tries to learn to read quality as a human being would. But the backlinks are still its core. So I cannot really say, it's hard to keep up, since the major part of it has remained the same. Thus, if you were doing it right 5 years ago, you are most likely to be just fine today!
I wouldn't purchase a purely SEO product these days. SEO is heavily integrated into usability, content, PR. It should be purchased together with a higher-level service. You can no longer rely on pure rankings: You should pursue other channels including social media marketing, outreach, building strong content assets: These all improve the overall authority (and hence rankings) of your site. Don't invest into SEO alone (it wasn't a good strategy earlier and it has become pointless these days).