The Red Sox acquired Andrew Bailey last winter in one of Ben Cherington's first moves as general manager. At the time, Boston was trying to replace Jonathan Papelbon, and had to do so on the limited budget that Cherington inherited from his predecessor, Theo Epstein. This meant trading low-minors prospects and a major-league player in Josh Reddick in order to pry three seasons of Bailey from the A's.
Now that Boston is no longer stuck in that kind of financial situation thanks to the Nick Punto trade, things could be different. Or, at least, the Red Sox would like them to be different. Buster Olney:
Rival teams say that Red Sox open to dealing Andrew Bailey--but because his value is currently low, odds of them trading him are pretty low.— Buster Olney (@Buster_ESPN) November 27, 2012
Bailey missed most of 2012 after a collision in the spring broke his thumb and cost him months of the season. Upon his return, he was still missing bats, but he was rusty overall: eight walks in 15 innings, along with a pair of homers, led to a career-worst 7.04 end-of-season ERA.
The key there, though, is "rust" and 15 innings. It's not as if Bailey pitched the whole year and was a disaster that cannot be relied upon going forward. The problem is that, like with Jacoby Ellsbury, Boston could absolutely trade Bailey and get something back. But since their value is at a low point due to injury, and concern about both future injuries and the repercussions stemming from the last one, they won't get as much as they'd like. Ergo, Bailey, and Ellsbury, are both likely to be Red Sox in 2013 unless a team challenges that perception.
While Boston's bullpen does have plenty of quality options in it, Bailey joins Junichi Tazawa as one of the only arms that can be trusted at the back-end of the pen (remember, Scott Atchison's elbow might be an issue), so getting rid of him might not be in Boston's best interests, anyway. Lest they plan on bringing in another dependable, high-quality reliever, anyway. Since Tazawa has just the one year in that role, and Mark Melancon's last two months of strikeout-fueled pitching aren't quite enough to be convinced of his return to pre-2011 form, Bailey should be of plenty use to the Sox.
In essence, the Red Sox don't want to deal Bailey because they don't think he'll be any good after just a 15-inning sample. It's just that, were he at full value, they'd love to move him in order to get something significant back.