Sometimes you may see a website with a really good PageRank, generally 6+ that you would get a great deal on. Maybe you are purchasing only a link on the website, the domain-name or even the entire website. You purchase it and a few weeks later the PageRank drops heavily. What happened? Did the backlinks just disappear over night?

No. Most likely the truth is that there were never any backlinks pointing to that domain-name, and the PageRank you were seeing was artificially inflanted. This is most of the time done by applying a 301 or 302 redirect - also known as a permanent redirect - for that domain-name to another website that has a very good PageRank. This way, in time, Google gives the redirected domain-name the same PageRank as the website it points to. Even after the domain-name no longer points to that website, the PageRank will still show up for a good while until Google does a PageRank update.

How can you spot a fake PageRank? Search Google for "Fake PageRank Checker" and you will find a great number of tools that check the actual PageRank behind an URL.

Many times you can also spot a fake PageRank just by looking at the number of backlinks and their quality. If you see a PR7 website having only a handful of links, none of which are very highly ranked, it's most likely an inflated PageRank.

If the URL is still pointing to the website that's inheriting the high PageRank from, you can check if it's redirected by looking at the headers. If the headers don't start with "HTTP/1.1 200 OK =>"  (200 is the all-ok HTTP status) but instead it starts with a 301 or 302 status, you are being redirected. However, be aware of cloaking which is a simple scheme that only redirects requests coming from the Google Crawler. Therefore, PageRank inflating can be even more dangerous and difficult to spot when one is redirecting all requests by the Google Crawler to a highly ranked page (so that the PageRank gets inherited), but the visitors get pointed to a different location.