Originally Posted by
icefractal
And how does that square with the part about getting a +0 to +6 bonus on the Charisma check based on the task and reward (which you "perhaps" offer or perhaps not)?
If the creature can simply veto any deal it doesn't like, then why is it making a check to refuse service? If it doesn't want to serve under any circumstances, it can simply decide any possible deal you offer is "unreasonable".
Also, more circumstantial, but opposed Charisma checks are not how normal negotiations work. So it's not like you're just putting them in a circle and then convincing them as you would anyone else.