As noted elsewhere, do everything you can to avoid handing your card to anyone.

For online purchases, do everything you can to avoid giving your card number to anyone - use ApplePay / GooglePay / Amazon Pay / PayPal etc. wherever possible. These can be used to put charges on your card without giving your card # to the merchant. These are one-time authorizations (unless you explicitly identify it as a subscription / recurring charge), so they can’t reuse the transaction token they get.