With the new Paizo Webstore, your order payment is immediately captured when placing an order. This is normal and expected.
If your order payment fails, you may see a "pending" charge on your credit card. This is a credit card authorization - your bank has "reserved" those funds in your account for an order that never actually completed. This happens most often with AVS Failures (see below). These pending charges will drop from your account within 2-3 business days, per your bank's policies.
AVS (Address Verification System) Failures occur when you try to make a purchase using a billing address that does not match the registered billing address on your card. Paizo does not have control over these failures - any time they occur your bank is telling our credit card processor that your billing address in your order is incorrect. Please double-check your billing address and check with your bank to make sure you have the correct information. AVS Failures generally result in credit card authorizations, and multiple attempts to purchase with a bad billing address will result in multiple pending charges on your card.
For more information about authorizations and authorization holds, check out the Wikipedia entry on authorization holds.
To contact Paizo Customer Service, email customer.service@paizo.com or call us at at (425) 215-1442 (Monday–Friday, 10 AM–4 PM Pacific Time).