Firefox has a tool and i think its called SeoQuake. I used it once and it was able to tell the PR of any site i visit.
There is no such tool from where it becomes clear that PR is fake or real. Visit the site daily basis, then you can analyze the exact PR. Actually Google always update the PR after 3-4 Months, so in between this time , some of the person show the fake URL to get publicity.
Check the domain in the site called checkpagerank.net On this site you will even all the details related to that domain, like the total number of backlinks, how old is the domain, all the web history of the site as well as if the pagerank is fake or real. For quick way, you just have to type in google, info:domain.com
the best way is to use multiple pr checking websites i use webseoranks.com, because it's accurate and gives more stats about the website
Use the Google toolbar to check the PR and use: info:yoursite.com At google.com and make sure it shows the same domain. -- Alternatively you can just not care about pagerank...
there are many tool and online sites where you can check valid PR so just try to google >>> check live PR
PR overall means very little these days. Spending much time worrying about it is probably counterproductive because it doesn't tell you much. G does not broadcast how they are ranking you anymore.