This is what I know:

If you're Neutral, the BB guards SHOULD defend you if someone else attacked you, unless they have a higher reputation. If they do, I hear the Guards will attack the one with lower reputation. I've been the defender in BB several times, and a few times the guards attacked me rather than the aggressor.

I think the highest discount you can get is the 10% at Honored. The WoW FAQ on it doesn't say that it increases. Granted, it's likely outdated because it doesn't have 'Exhalted' on there. No additional money for higher status when you're selling things.