I am aware of at least one robbery in which the punter left to get something, then came back with his friend - so I do get anxious.
The last time the notes changes (around 10+ years ago) a punter turned up with his stash of old notes, fair enough the bank would accept them but shops were not and I just did not like this attitude that he could get rid of them by giving them to me. Perhaps I shouldn't have been so pedantic? He went to the cash machine obtained new notes, but shortened his booking and reduced my fee by the half hour he took to go to the cash machine.
Another guy did the meet for coffee at the start of the booking, extended then on the way to my incall place said he needed to go to the cash machine. I cannot remember if I had taken payment up front, or the booking had been a coffee only. Anyway I held my breath, and I do not think he realised how much anxiety doing this created for me.
A drug/stoned punter 'lost' his stash of cash when he wanted to extend his short booking (I could clearly see which item of clothing it was hidden in but I was not going to tell him, because I just wanted him off my premises). He came back knocking on the door 5 minutes later having found it in his sock. I refused to let him in. He actually turned up another time totally unannounced, knocking on the door whilst I was in a booking with someone else.
Also had the money in the car reason at the end as well as at the start of bookings, all came back but some of these anecdotes are a lesson to always take money upfront unless you are prepared to lose it. The end guy did not even think of the distress it would cause, even boasted of the trust I showed him.
Re bank transfers I send a text when I accept a booking with a new, or second booking client - confirming receipt of deposit, time, date, location, duration, balance to pay cash on arrival. If someone asks for transfer I stipulate must be in my account, viewable on my online banking at least 2 hours prior to the booking.