There are a handful of things you should know before you approach one of these people to publish an article.
First, PageRank (PR) has had a declining value as a metric since 2013 (and is pretty much non-existent today) as Google hasn’t publicly updated PR since December 2013. Because of this, any tool that measures PR will be giving you data that is over 3 years old. What that also means is that anything could have happened to this site that could have affected its PR (both positively and negatively) within that time period, and you wouldn’t know based on its PR.
This isn’t to say that Google is no longer using a form of PR in one way or another behind the scenes. It means that Google won’t let us know the metrics they use in determining the value of a site.
There are several options out there that can help you determine the actual value of a site. Just keep in mind that these sites use their own value system and metrics that Google may or not follow. The most commonly used tools are Open Site Explorer: Link Research & Backlink Checker (Moz), Marketing Search Engine and SEO Backlink Checker (Majestic), and SEO Backlink Checker & Competitor Research Tools (ahrefs).
All of these tools utilize their own metrics, though, so one site may look great with one tool but not so great with another. Of course, there are sites out there that also block these tools from crawling their sites, so the information could also be misleading.
Each of these tools offers a free account; however, the free accounts are heavily limited. Paying for each account, unfortunately, could equal hundreds of dollars per month.
Backlink Profiles and History
Every site that has any value has backlinks. There is no way around this. If you’re asking about backlinks from high authority sites to your site, you already know this.
It’s important to know that the site that is linking to your site is clean. This means that this site needs to have clean backlinks pointing to it from other sites. Again, you can use the above tools to see a limited number of crawled links to these sites (assuming you know the URL of the site you are looking to pay for an article to be posted to). When you check on those backlinks, you should be looking to make sure that the links aren’t ‘spammy’ or coming from questionable sites. Anything pharma, pornographic, designer handbag, and more could mean that a link from this site could be toxic to your site.
A clean backlink profile will mean that the links pointing to this site come from sites that are similar to the subject of the site. If the site is about real estate, the majority of the links pointing to it should be from other real estate sites or blogs.
Along with this is the actual history of the site. You can use Digital Library of Free Books, Movies, Music & Wayback Machine (archive.org) to see the crawled history of the site in question. Here you can actually access and view the site as it was at the time it was crawled. Like the backlink profile, if you see anything that looks out of the ordinary, it may be toxic to obtain links from this site. This is because if the site looks great today but was a Russian casino site 4 years ago, it may have links pointing to it from Russian casino sites - which could be toxic to your site.
OBL stands for outbound links. This is important to know because the more links on a page, the less the value of each link. If someone is offering to post your article on its ‘PR9’ page for $15, you can bet that there are likely many people jumping all over this ‘opportunity’. Some of these sites will have articles roll off the front page and into the inner pages, but there are others than just have one page of 100 or more articles.
Of course, today, as of the time I am writing this, everything written here is valid. That doesn’t mean it will stay that way tomorrow.
For instance, I have recently read that Google may automatically disassociate links to a site if the link doesn’t match the niche of a site. For instance, a site was a golf club sales site and had hundreds of links from golf-related sites, but it is now an interior decorating site - Google would know that the old golf-related links wouldn’t be valid for interior decorating, thus voiding the value of those links. Take this one with a grain of salt because I haven’t seen any evidence of this - just something I read (though, I can’t find the article again which is odd).
If someone is offering to post articles on sites based off of PageRank, avoid it. If this person is using a 3-year old metric that Google has told us they are no longer using (Google Confirms Toolbar PageRank is No More | SEJ), they may also be using 3-year old SEO strategies that are also no longer valid.
On top of that, a site that was PR5–9 back in 2013 were valuable. To be offering real estate on such a ‘powerful site’ for a few bucks is a red flag.
I say avoid these types of SEO tactics.
That and Google frowns on buying links. And we all want to make Google happy, right?