Last year, as I was checking the licensing and attribution on the tracks in my soundtrack library for Lunatics, I came across a bizarre and rather disturbing practice: bait and switch licensing as a ploy to sell music. This is a truly weird idea, if you understand what a free-license means, and it's deeply unethical, but here's what I think is going on: the artist (or more likely, some intermediary, such as a small record label) gets the idea of using a "free" loss-leader to try to draw people into buying a commercial/proprietary album. This is okay in itself, but the problem lies in that confusing word, "free".
They're not thinking of "free" as in "freedom", but as a price. So, they think they can give a work away and then take it back. Legally of course, this is nonsense with a Creative Commons license -- once you've released under a By or By-SA license, you cannot switch the license to By-NC-SA or "All Rights Reserved". Once the work is out there, it's free.
But how do you prove that? That's the part where this gets unethical: The standard answer is that I check the "verification URL" -- but the producer has given me their sales website as that URL. And they have changed the license since I downloaded! Oops.
How can you protect against such a threat? I'm not sure if there is any absolute way, but I decided to give myself a little bit of evidence by using a screen-capture tool to grab the webpage of album pages as viewed in my browser. Of course, I'm entirely capable of fabricating such evidence, so I'm not sure how solid it would be in court. But at least it's something.