Would you rather have mediocre (or worse) service from someone who is very deferential to you, or excellent work done by someone who is more crusty?
Excellent service from someone nice would be ideal, but we can't always have the ideal. And we don't know until the work is done whether the crusty person was an irritable genius or just a jerk. But let's say you've established a track record for each provider. Who gets the nod? Mr. Results or Mr. Nice Guy?
Oh, and the cranky one charges a little more money, too.
Who wins? Competence or charm?