Rip-off card fees were meant to be a thing of the past thanks to the interchange fee cap.

But when purchasing a flight from London to Japan with Air France earlier this month, I was shocked to be faced with a bill of £6.20 for making the purchase with my debit card.

It's not just airlines at it though. I've found concert and theatre ticket booking websites as well as car hire companies are surprising shoppers with fees for paying by card at the checkout.

So I decided to delve into the matter to find out what's going on.

What's a fair charge?

The cap on card interchange fees (that’s the charge that the your bank will impose on the retailer's bank) is set at 0.3% for credit cards and 0.2% for debit cards under the Consumer Rights (Payment Surcharges) Regulations 2012.

My flights came to £422.70, meaning that the interchange fee was only 85p at most. So why was I charged £6.20 to pay by debit card?

Giles Mason from the UK Cards Association said: “Retailers can currently add an additional fee to a customer’s bill when a credit or debit card is used for payment, but these cannot considerably exceed the retailer’s processing costs for the payment”.

Basically, this covers the Merchant Service Charge, which includes the interchange fee and can include the cost of things like hiring card terminals, employing staff and covering overheads.

It’s trickier to break these costs down as it depends on the nature of the merchant’s business and how it operates.

What the charge actually covers varies pretty wildly, and there's very little transparency. That's where the problem lies.

An unregulated playground

When I tried to find out more about who deals with monitoring the remaining charges, it seemed like I was passed from organisation to organisation without much in the way of solid answers.

You see, the Payment Systems Regulator (PSR) is only responsible for making sure that the interchange fee cap is enforced; it doesn’t have any power over other parts of card payment charges.

“It’s very hard to gauge,” says David Stewart of the PSR.

How to fight back

Stewart says that “everyone has a role to play” when it comes to fighting punitive fees.

For example, retailers can shop around different banks to find out what’s included in their Merchant’s Service Charge so that they can get the best possible deal and pass savings on to their customers.

And we can stop shopping with retailers who have high debit card charges to discourage them from charging high fees. For example, instead of paying 50p for ordering through JustEat by card, call up the takeaway direct to make your order.

But more than that, I think that regulators need to be given more power over Merchant Service Charges, with easy access to what each charge includes. It would also help the public to know where the card charges they're paying actually go.

This article reflects the opinions of the writer, not any corporate view held by BT.

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