A Thief/Diplomat player in one game was upset that he neg'd down a roll to Influence a contact. "All I wanted to do was buy even a friggin' magic dagger! If I don't, then how can I fight all these demons you're throwing at us?"
I let him know that this particular contact was still a friend, but he wouldn't help with
this inquiry. So he didn't lose the contact or even
tick him off. But this guy would "never" help him find a magic weapon to fight demons. Maybe he lost a son to a demon after giving him a family heirloom to fight demons. Who knows?
Like yamma said, use the chart as a starting point. If you don't think it should apply, change it! Maybe the proprietor will not consider buying meet from the PC, but he might sell him a wagon or whatever. Friends fight and argue about stuff from time to time. Just because they have extreme differences on one point, it might not totally spoil the relationship.
Let the PC's know that you give a bonus for bribes.