Over the past few years we've had multiple stars in the NBA looking to get traded. First, It was Carmelo Anthony, who despite his flaws is a legitimate star in the NBA. Analysts everywhere all said he would end up in New York (Knicks), and he did, so now it seems to be convenional wisdom that if a player wants to go somewhere that's where he'll ultimately end up traded to.
But if we look at another three stars we'll see a stark contrast. Chris Paul wanted badly the end up in New York (also Knicks), he ended up getting traded to LA (Lakers). Thank God for Stern btw. CP3 is now a Clipper. Dwight demanded to get traded to Brooklyn (not Knicks, woohoo!), but again he got traded to the Lakers. Granted he could have walked to Brooklyn, but the Magic never had any intention of trading him here, which is the point of this post. Josh Smith, though not publicly saying it, probably wanted to end up in Brooklyn too (my opinion only), and every analyst also said he would "ultimately" be traded here. But he didn't.
I think the lesson to be learned here is to never trade junk for star players. You always want have an attractive package. It's how the Knicks acquired Carmelo, and how Both LA teams acquired Chris Paul. Teams just don't like getting screwed, and might decide not to trade just out of spite, prefering capspace over nothing.