Surcharges are added to most purchases, but what are the rules behind these extra fees?

You head to the register at the cafe to pay for your lunch, swipe your card and suddenly realise you've been hit with an extra small but unexpected charge.

It might be listed on your receipt as a service or merchant fee, but either way it's because you've used a credit or debit card.

With the pandemic accelerating the use of cards instead of cash -