So Facebook has introduced an ad library and you need to check it out immediately - https://www.facebook.com/ads/library. In the spirit of full transparency you can now search for all ads run by page/organization OR topic OR theme. It is a complete library of ads run, active and inactive. The library is available now, but there seem to be hints that in addition to showing the ad you will soon also be able to see amount spent and reach (although this may only be rolled out for political ads).