*applauds John*
For me the term sell-out varies, from the lazy type sellout that John mentioned, to the money based sell-out that neoteric mentoned. I can think of a couple of people that are odd fits in both categories, one is Green Day with their American Idiot alubm, while (I think) it's a good album, I also feel that they some how managed to sell out to the prevailing emo image, even though they had the punk/emo image all along. The other example is Feeder, their most famous song, Buck Rodgers, is clearly an example of somewhat lazy songwriting, and yet rant has proved over several albums he can write a damn good song - the key to Buck Rodgers is that he wrote it for another band, but when the band manager (or label) heard it they realised it was too good to let go.
So that muddies the sell out waters yet more!
But is there anyone with examples of my original question? (Not to close off the discussion, but I'm entertained by the question) Please note that it can include any aspect of songwriting, so the 'could be better' phrasing that Anne mentioned is exactly the kind of thing I'm talking about