You should probably check if the PR is real or fake. You can do this by verifying the number of backlinks that the domain has. If it has a lot of backlinks then the PR is probably legit, if not then it's fake.
Go to http://www.checkpagerank.net and check the domain, it can give an assessment if the PR is valid or not.
With regards to the price, I'm not sure if $150 is a good deal, maybe others can give their opinion about this.