You want to buy a book that costs $30 everywhere.

No matter where you are, you will always pay $30.

However, I assure you that you won't feel as though you are paying the same $30.

It feels more expensive to pay with cash than with a credit card.

It feels more expensive to pay with a credit card than with a mobile phone or QR code.

It feels more expensive to pay with a mobile phone or QR code than a contactless payment.

It feels more expensive to make a contactless payment than to make an online purchase with a credit card.

It feels more expensive to pay with an online credit card payment than a stored credit card.

The way customers act changes how they think about price.

The payment method can be a value proposition for your product. Because we are not rational thinkers, marketers' job is to find insights into customer behavior and hack it to make it easier for them to buy.