Paul, I couldn’t agree more. I start with a minimum charge then give a reasonable estimate if I think it will take longer than a couple hours to prepare, based on an hourly rate. Assuming there are no surprises, I will charge the rate I quoted.
One of my newest clients came to me after her long-time tax preparer charged her to file Form 2210 even though they were the ones who underestimated what she should pay in throughout the year. Nice!