Sometimes my customers are a pleasure to work for.
I do a big place about 15 miles from here. Its £190 every 3 weeks.
I invoice them every other visit.
I did them yesterday for the second time and invoiced them just before I set off to do them, for £380.
The posty has just been and a cheque has just arrived for £380 from said customer. You can't knock that.

Although I have no individual jobs of that price, I would say that about 40% of my customers pay as quickly as that. Another 40% take up to a couple of weeks (that's fine by me) and another 20% drag their heels a bit - a few of them badly so.
So if my cash flow is tight and a load of work is overdue, it doesn't take a genius to work out which customers will get priority.
Like yourself, I have some absolute gems of customers. If I do a job and receive a cheque within a few days, I do feel genuinely appreciative.