I always have full payment visible in an open envelope on the nightstand as I know many other people do.
My view is I have booked his time & therefore I will pay even if the service isn't as good as I hoped. My option then is not to book him again & maybe post a negative review.
If he is a gentleman he won't pocket the money until the appointment is finished-in fact the best times have been with guys who followed this protocol & were therefore re-booked & good reviews posted.
Guys I have previously booked have told me there's no need to display the cash but I still do it cos I want him to relax knowing he will be paid in full & I can always slip an extra bill or 2 into the envelope if I wish to give him a tip.
Those whose service was not so good have always pocketed the money immediately!
Bottom (!) line-the labourer is worthy of his hire & I want the good ones to welcome a request for a subsequent booking