A customer claims they did not authorize a POS transaction on their ATM/Debit card. We open a claim and find out it was a pin-based transaction. Is this good enough to make the customer liable for $50.

I don't recommend you hang your decision on this fact alone. There are too many card-skimming and shoulder-surfing scams out there to say with a certainty that card plus PIN means customer did it.

You might ask the customer if he/she had ever allowed someone else to use the card and PIN. Look at the customer's use pattern and see if the challenged transaction fits the pattern or not. If your customer is in his/her 60s and routinely uses the card only at Springfield-area supermarkets and gas stations for purchases under $100, would a $350 purchase at Newbury Comics in Harvard Square fit the pattern?

You can assign the first $50 in liability to your customer only if the customer failed to notify you of the loss or theft of the card within 2 business days of his/her learning of the loss/theft. This is always a touchy issue, since proving when to start counting these days is difficult. Is part of your incident interview script "When did you first notice that your card was missing?"

Thanks, John.
What you said makes sense. The customer did not lose the card, just says she did not do the transaction. It's not a large amount so we'll just take the loss, but this is happening more and more.