How does Google know if a backlink is good or not?

[activitysuper]

Hi,

What does Google look at when assessing a backlink?

How important is it to get a backlink from a website with relevant content?

Ex:

1. Domain/Page Auth 80, website is not relevant. Does not use any of the words in your target term in any area of the website.

2. Domain/Page Auth 40, website is relevant. Uses the words in your target term multiple times across website.

Which website example would benefit your SERP's more if you gained a backlink? (and if you can say, how much more would it benefit - low, medium, high).

[AndreVanKets]

Relevance is important, but then so is the domain authority and trust.

A link from a news website for example. Its unrelated, but can provide a powerful boost for your websites "trust"

Your main objective in my opinion should be to get links on relevant websites, however you can mix the two by getting links from high authority, unrelated websites as well. There are a few guest bloggers on SEOMOZ who link to their companies websites totally unrelated to SEO,

lets say you already had a mix of relevant as well as unrelated high authority links and you had to choose between DA80 (unrelated) and DA40 (related)

I would go with the most powerful site, DA80

Greg

[activitysuper]

Thanks for reply Greg.

Glade you mentioned Guest blogging because that's what im talking about really.

Yeah I spoke to Ann Smarty from My Blog Guest and she agreed, DA over relevance (to a certain extent).

What happens though if you guest post 5 articles to say DA60 blogs where your in travel and the blogs are in SEO?

I would have thought 5 guest posts on DA40 blogs where your in travel and so are the blogs your posting on would have worked a lot better.

It's a tough one for me.

[josh-riley]

Based on my conversations with Google, relevance is absolutely something to think about - if your site is all about oranges and you get links from sites/even blogs that are all about cars, it's  flag because it can look spammy.

Unless it's an outlier and is just one (or two) random links from sites that aren't related in content to yours, you risk harming yourself by connecting your site with unrelated content.