Over a decade ago there was a mix up with a pub with rooms booking I had made with booking.com. It was the pubs fault, they had copied the booking by hand into their diary on the wrong day. Luckily I had the printout with me and was able to prove my booking date.
They were full, but were able to put us up in a B&B across the road. It was shut for refurbishment but two rooms had been finished and we were comfortable accommodated. The original booking had been for a room only but we got breakfast at the B&B so all in all a good outcome.
When I got home I checked my bank statement just to make sure I hadn't been charged twice and saw to my horror several small outgoings over the previous 48 hours, amounting in total to around £1000. The payments were linked to my Paypal account and Paypal reimbursed me in full, with the separate amounts reappearing in my bank account over the next few days until everything was square.
Around the same time I started to receive emails from people accusing me of putting goods up for sale on Ebay and not sending them. The amounts stated by the people were identical to the amounts taken out of my account.
To this day I cannot fathom out how this was all connected (I'm certain it was) and despite being very happy with Paypals service I have not used them or Ebay since.