I have had the opposite. Horny as fuck, shag hard, come. Still so horny. Blowjob epic, come, still horny. Etc. hot day really horny...just can't get enough and sate the horniness and get rid of the wood. Those days are great if you're with a civvies you picked up in Hyde park on a June day, but when paying for the hour and she wants you gone after 60 minutes, no so much. Leaving a punt hot and horny isn't good.
I guess in your example, it's hard to have a rocket with enthusiasm if you dont fancy her at all. Even when you don't fancy her, it'll be fine if she has a nice torpedo tube, or a nice fibre pipe, etc. If she has an old meat grinder for a pole warmer it's blowjob time or time to go home.