I've thought of another couple!
When I went from temporary to permanent at one job, I wouldn't have been paid for 6 weeks (temp wages were fortnightly but as I'd missed the date the accounts were done I wouldn't get paid on the permanent contract until the end of the following month), so the lovely little old lady who did the accounting said she would pay me 3 weeks wages this month and 3 weeks the next month. I agreed to that because it was still £375 which was a lot to me whilst still a student.
So she wrote a cheque from the company account, but mucked up and gave me the full £500. When I pointed it out she suggested I bank it anyway and next month she'd put down to pay me £250 instead, would that be OK. I decided as long as I budgeted well it would be fine.
You can guess where this is going, yes?
The next month I got paid by BACS - £500. She was on holiday and when she got back I forgot to mention it.
I worked there for another 2 years and was never asked for that £250 back. They're still in business, and the boss used to letch at my cleavage, so I don't feel bad.
In my current job I sometimes opt to take unpaid leave for things like when DS is ill etc. My manager and our department secretary logs this and sends the details to HR, who blatantly ignore it and pay me anyway, without reducing my leave allowance. I've rung HR before and the woman who I'm assigned to always gets snotty and says it can't possibly be wrong because 'the computer works it all out'. Except they've made major cock ups before like thinking I'm off sick and putting me on half pay when I've not been off sick in weeks. So I think it's a problem with the HR woman who puts what the Secretary sends into the computer as I've seen what the Secretary sends her and it's correct when it leaves her office! The result is I get extra days of paid leave and can't get it put right. What a shame!