This technique has become so popular and people with PR 0 create a fake PR 8 or 9 and start selling links, they usually target the people how are new to internet as well as search engines techniques and they pay high for something that worths nothing.
 
This trick is now used by many cheaters who cheat people by saying that their pageRank will be increased if they their high ranked (pagerank) domain points to ehri site, Its true that if high pagerank site point another site, google considers it as a vote of confidence, but what if the site pointing to you has pagerank of 0 ? Its useless even harmful if the site has been banned from google.
 
The problem occurs in google toolbar, you can cheive high pagerank by simply redirecting with 301 header redirect method, redicrect site to high pagerank site for example google.com itself, then wait after the next pagerank update WOW your pagerank becomes exactly to what google.com have.
 
you can check either they have any backlinks by the using the following query in google
 
link:www.websitename.com
 
the above query will return all the backlinks ofthat particular website. here is a free tool which can tell you the actual pagerank of any website
 
 
So be careful when you are buying links just to increase your pagerank from a high pagerank website, before buying check if the site has any backlinks in google, if the site has pagerank 7 and there is no backlink then it has a fake pagerank, so its useless and waste of money.
 
My suggestion is not to buy links to get you pagerank high, becuase you will be cheated and just stick with your relevant websites even if they do not have high pagerank.
 
Search engines like google.com have become very tricky and picky, their system can quickly identify if you are spamming and getting links (buying a lot of links) very quickly. Keep it natural, if you will buy a lot of links you will harm your ranking, and dont get links from irrelevant websites becuase those links not considered as vote of confidence and bots can easily idently it as a link trade.