Now you can
pre-authorize transactions that are placed in your online shop and
charge them at a later time. With this option enabled the system will
pre-authorize a customer's credit card for the value of the goods
purchased. You are then required to login to PayPal and complete the
transaction by either charging the card (so you can receive payment) or
cancelling the transaction altogether. This feature is useful if you
carry a limited number of units for each product and you wish to ensure
you have stock before taking payment from a customer.
To enable this feature go to: eCommerce->Payment Gateways.
You will see a new checkbox in the PayPal Website Standard