I imagine there is a general aptitude for the job as in any role in life, along with some mentoring would for sure help. Forget 10 days quarantining when they get off the boat, they should have a crash course on pleasuring a man!
I am certain fatigue after 4 days on the trot sets in, but why do they care if the man leaves satisfied or not if they are making 1k a day? They haven’t realised the need to build up a loyal regular base yet, as they are still the new shiny toy everyone wants to try out for now.