All joking aside, have you ever tried to define a sell-out? Two things come to mind when I try to answer this question, and I hope my analysis will better equip you to communicate your concerns to your favorite artists and their respective agents, managers, and business executives.
The first is a financial sell-out. This is most readily identified by a connection to a third-party commercial product. Depending on the artist's intentions and goals, this may or may not be selling out at all. In the Information Age, art is cheap to create and distribute, provided you find your creative spark, and it follows that the end product is expected to be inexpensive or even free.
This doesn't mean that the artist is bound for poverty, it just means that he or she must also creatively leverage the art to develop revenue. This concept of leverage is foreign to most people in the "work-a-day" world, but entails connecting a third party (who has something to sell) with your fanbase. There are many ways to execute this, but basically the artist earns a commission of some sort off the sales made because of his art.
For this not to be a sell-out, the third-party has to share the same intentions and goals as the artist, and be offering a product that the fans actually want. While generic sponsorship (i.e.: fast food corporations) might lead to short-term revenue, the reputation of the sponsor becomes an issue. When the fans dislike the sponsor, they feel abused by the artist. This has a long-term degenerative effect.
Which leads me to the second, and more critical form of selling out: the compromise of one's principles. To gain any sort of fanbase, a creator must be equipped to create art which resonates with a number of people. Basically, to "resonate" is to be harmonious with certain universal truths. The wiser the artist, the more universal the art, and the greater the fanbase. (This is different than formulaic elements, which only superficially represent real life.)
When an artist gets comfortable and chooses to stop pushing the envelope of his art, he relies more and more on what worked before. This, in my opinion, means he has actually stopped being an artist entirely. To stop uncovering universal truths or expressing them in new ways is to compromise the very thing that makes your creation a work of art. That being said, the main issue comes in making that choice. Every artist hits a wall from time to time and must backpedal to find his way again.
One must remember the natural cycles of any business, and art is ultimately a business if it's not a hobby. As the überfans naturally share what they love with those who don't yet know or understand, the balance will naturally shift away from a heavy concentration of überfans to a general and mainstream appreciation. This is not selling out, but moving on. Some überfans may move on as well, because the less they feel they're part of an exclusive thing, the less they care to be a part of it.
Ultimately, I think selling out means betraying your fans, especially your überfans. If you can't sell the vast majority of your überfans on the change, then you've bitten the hand that feeds you. On the other hand (pun intended), if the change brings your art closer to its FIT state, then your fans will either come around or they weren't true fans—either way, you'll increase your überfanbase.
FEATURED MEDIA: Adaptation - Screenwriter Charlie Kaufman is given an assignment to write an adaptation of a book. This not being what he usually does, Charlie can't help but write a crazy story about a secret love affair and drug trafficking mystery, which himself and his fictional twin brother are forced to solve.