If my customer pays by card, can I add the card charge on top instead of paying it myself?

Yes, in most cases you can pass a card charge on to the customer, but whether you are allowed to depends on your payment gateway and on the rules in your country. The booking system can add a fee on top of the total at checkout, either as a fixed amount or as a percentage, and show it as a separate line so the customer can see what it is for. It can also be tied to one payment method only, so a customer paying by bank transfer is not charged extra while a customer paying by card is.

Where this gets restricted is not the software, it is the card schemes and the local law. Some countries do not allow a surcharge on debit or credit card payments at all, and some gateways say plainly in their terms that you may not add one. In those places most agencies build the cost into their markup instead, so the price the customer sees already covers it and nothing extra appears at the end. That is quieter, and it usually sells better, because a fee that turns up on the last screen is a common reason people walk away from a booking.

It also helps to keep two things separate. The fee you are charged and the money that actually lands in your bank are not the same number, because the gateway normally takes its cut before it settles with you. Your reports should show the gross amount the customer paid, the fee, and the net you received, otherwise your accounts will never tie back to your statements.

Before you switch a surcharge on, read your gateway agreement and check the rules where your customers are, then decide whether you would rather show the charge openly or fold it into your price.