So if it is a valid defense to say you bought a license in good faith but were lied to .. is it a valid defense for me to buy a pirated DVD and say I just thought it was a good price? I'm not convinced that would work for me.
It probably doesn't, and the only protection we have is to not try to buy anything that may have copyrights attached to it, as you can never check whether a license is valid or not. E.g. you buy a CD off e-bay, seller claiming it's a second hand one, thereby validating the low price. But in reality this seller has been making illegal copies of the CDs he sells, so what you get is an infringing copy.
Another situation. About 20 years ago I was browsing CDs at a second hand CD stand at some pop festival. Lots of great stuff there, but I ran into a few albums, collections of current hits (well, last year's hits by then), which I happened to know were illegal. Pretty much all the others I assume were fully legal. Most people out there probably didn't know these were illegal, they were mixed with lots of legal stuff, and sold at the same price. Hard to argue wilful infringement.
Closer to home: all those copy-handbags and copy-watches. I don't know many luxury brands, and those that I know I only know from the name on the shop front. I don't know their design, much less care for what they do. I don't care much for fashion, and their prices are way out of my budget anyway. However if I were to browse a market looking for a nice gift for a female friend, I may run into a handbag or purse that I like, and that I think she may like. Now the problem is that I can't tell whether the design of this bag is a copy of some luxury brand. Am I truly expected to first browse all the shops on Canton Road and make sure I know the current designs there, before heading off to the Ladies' Market or Fa Yuen Street Market?
A year or two ago there was also this discussion on Slashdot about someone's uncle subscribing to a web site offering recent movies (often still running in the cinemas) in streaming format, like Netflix et.al.. This person's uncle paid for these movies to gain access - unaware that the seller didn't actually license them. The uncle was just happy to be able to watch these movies for a good price. It's hard to expect everyone to know how movie licensing works, or to know who the copyright owner is and to phone them to ask whether a certain service actually has the right to resell this movie to him.
It's easy to come up with many more similar situations - either from anecdotes, or my making up a realistic scenario where you think you legally buy something but in reality you don't. The only way to be safe is to not buy anything. No branded stuff, no unbranded stuff. No music, on physical media or otherwise. There's no way you can tell if it's real or not, there's no way to tell whether the shop owner is honest, and if the shop owner tells me it's legal and it's not, it's still me that's hit with fines or worse.
CBC should be let off for using the YouTube video for the 10 days they had a license for. They should be prosecuted for using the video after the license expired. CNN should be prosecuted for selling this license - which imho is even worse. CNN not only infringed on the copyright of the maker of the video, they directly made money off of it, and they sold something they did not own (which is a totally separate issue and has nothing to do with copyright as such).