I did some babysitting on Saturday night. When the couple got back they said sorry they didn't have any cash and they would transfer me the money. It is Tuesday and in spite of giving them my bank details, and a reminder text, still no payment.
If I ever babysit for them again (not sure I will now), I will say I will only do so if they pay cash that evening. Sadly this kind of way of operating seems common amongst middle-class people. It may not be a big deal for you to wait days for a relatively small sum of money, but it is for many others.