According to a comment in DigitalPoint forum, buying traffic from traffic brokers for an adsense site is a risky business. First, 99% of the traffic brokers will send you bot generated traffic that will just increase your impression and not giving you any click. Second, you will risk your adsense account getting banned for artificially inflating the adsense stat.
http://forums.digitalpoint.com/showthread.php?t=1585886