Basically BoAs should be set to where you pay to unlock them from the vendor and there set to your Battle.net so there unlocked on all servers.
Ex: A lvl 85 warrior uses his justice points to unlock a leather boa shoulder piece on BlackDragon Flight Server. Then he logs onto Mannoroth Server makes a lvl 1 druid, visits the BoA vendor and can pick up the leather piece for free to use on said lvl 1.
To prevent people from buying and then selling them back as some exploit they should be one time buy and made permanent so people have to choose wisely on what pieces they want first to last. So once they pick something there's no going back on the choose.
Also a BoA vendor should be placed in the starter zones so people don't have to run to the main cites to pick them up