Pay, book and keep the receipt
A few checks now can spare a second trip to the counter.
Ask before you reach for a card
Check the payment methods at the business or machine you are using. Keep a modest cash reserve for places or top-ups that need it. A transport card and an overseas bank card serve different purposes; do not assume that tapping one will do what the other does.
Check the item and total
Before confirming payment, look at the quantity, date and any add-ons. Ask about wrapping, cooking, equipment or reservation charges when they matter. Keep the receipt until you know the purchase is right, and take care not to leave the card on the counter.
Read the cancellation line
For a train, show, tour or room, check the cancellation deadline and the fee after it. Look for the time zone and the booked date, especially around midnight. Keep the seller’s confirmation and reference number; a search result or an uncompleted checkout is not a booking.
Have a plan for online booking
Some services ask for a Korean phone number or local identity verification. A tourist SIM does not promise access to either. Look for a visitor booking channel, ask the operator about a staffed counter, or choose another service. Enter payment details and passwords yourself.