A no-holds-barred article on the US-based Bill Hartzer Blog shows how dangerous it can be to employ “Search Engine Optimisation” services of dubious quality. I have to say that within that group of people, I’d include many of the so-called “full service digital agencies”, which is often marketing-speak for “we know a little bit about everything and a lot about very little”.
The article says: “Did you know that half of the search engine optimization techniques that were used only 5 years ago (maybe even 3 years ago) are now considered to be spam? Most of those SEO techniques are now listed in Google’s Webmaster Guidelines as being unacceptable. They are grounds for an algorithmic penalty or even worse: a manual penalty from Google.” So be warned. Someone could be doing terrible things to your website as you read this, just through ignorance.