For the convenience of our customers we accept a wide range of different payment types: Credit cards, debit cards, paypal and Amazon checkout.
Unfortunately, the financial institutions that operate these different payment methods charge different amounts to allow us to use them.
We always try to keep our prices as low as possible for our customers and the only fair way to do that is to make a small additional charge to those customers who want to use more convenient, but higher cost methods to pay.
It wouldn't be fair to ask customers who pay by debit card (the cheapest method) to subsidize other customers who prefer to use Paypal or Amazon Checkout (the most expensive methods).
We don't make any profit on these payment surcharges, we simply pass on a portion of the extra cost that different payment methods incur, which allows us to continue to offer our products at the lowest possible prices.