Quote Originally Posted by icefractal View Post
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.
There are times when an offer would not be amicable, but may still be within the realms of reasonable, and you need to consider the hostile nature of the spell. The charisma check, and it's bonuses represent a level of negotiation, hence why sweeter deals give you a bonus.