I worked with one client who ALWAYS paid late – in part because they insisted on paying by check via the mail. Whenever I asked about payment, they’d insist “the check is in the mail!”
At one point I visited the office, and talked to the staff accountant. I asked if it would be possible to switch to e-payment and they had no idea why that wasn’t the case already and put me into the system right away.
My next invoice was two weeks late for payment, so I contacted the client:
Me: Just to let you know, I still haven’t received payment for my last invoice.
Client: The check is in the mail!
That confirmed what I’d already suspected – they used the UPS as an excuse to not pay me on time.