In the battle forum etc. it is generally accepted that Lady Shiva and Deathstroke could defeat Batman so why don't they just kill him? There must be someone who would be willing to pay, do they have an underlying respect for him or do they just think it's not worth the trouble?
Not just limiting it to them two, just they the ones that came to mind, although I'm sure other could also be up to the task if they prepped for it, ie. deadshot