I have loads like this.
And when someone does something at my house (Greenthumb, an electrician, any tradesmen really) I never pay them on the day. Unless they ask.
If you're going to ask the custys to pay on the day-try and stay cool about it, they probably aren't doing it out if malice. Society seems to be using less and less cash, maybe they just don't think of paying you there and then.
Or, they may be really fastidious and keep all bills from one week and pay the lot in one go so they know who's been paid.
I used to have one customer who would photocopy the slip I left after writing the date on it, and send it to me with a cheque. He used to keep the original so he knew how many cleans I'd done.