They wanted to reassign Riker to command a starship for 13 years before he finally accepted the job. It seems like transfers are generally optional for successful officers who are in a position that works for them. If you're as unsettled as Sisko however, you don't get to say no when they send you off to command an alien space station in Space Siberia.
I always imagined DS9 as more so an old frontier style fort than Space Siberia..but I did laugh