the most common mistake people use is "window cleaner" I have a new one that's "mum's window cleaner" then you need to wait to narrow it down.
I keep a spreadsheet of all my customer's details, names, addressees, telephone numbers, dates cleaned, and have done since I've started.
When someone does that (uses 'window cleaner') for their reference, rather than their address for ours, I do a search on the spreadsheet for the name that the payment was made in, but sometimes, particularly with unmarried couples, the name doesn't tally with the name I have on the spreadsheet.
So then I look at the date. Generally, if someone pays on-line, I've cleaned their windows within the past five days. If they don't pay on-line by then, they generally won't and it'll roll-over to the following clean.
The amount paid is a big clue too.
It's a bit like a puzzle sometimes.