Why does a customer card appear to be charged after a void/decline?

It is important to note that when a transaction is voided, you are only indicating that the original transaction is not to be settled.

When you submit a transaction for authorization, the card issuing bank will place the requested funds on a hold if they approve the transaction. This is done so that, when merchants later settle the transaction, the held funds would be available to claim. Even if the transaction is not settled, the hold on the funds will remain until it is expired by the card issuer. How long these funds are held are entirely up to the card issuer, although the industry average is seven days for credit cards and three days for debit cards. 

Since funds are being held, this may impact the available balance on the card, and future transactions may be declined until the card issuing bank removes the hold on any authorized funds.

Authorize.Net® cannot remove existing authorizations from a customer's credit card. However, since the card issuing bank provided the authorization code, they will be able to remove the authorization. Card issuing banks may require the merchant to call or fax documentation, or may be able to assist the customer directly. Regardless of the card issuing bank's internal process for removing the authorization, they would need the authorization code in order to identify which authorization to remove. You can retrieve the authorization code by viewing the details associated with the transaction.

To locate the authorization code, please follow these steps:

1) Log into your Merchant Interface at https://account.authorize.net

2) Click Transactions in the main left side menu.

3) Enter one or more search criteria here. For example, you may search by the last four digits of the card number, customer last name, invoice number, or transaction ID.

Note: It is generally better to search using only one criterion at first and only add more if you see too many search results the first time.

4) Click Search.

5) Click the Transaction ID of the transaction in question.

6) A page titled Transaction Details will appear. The authorization code can be found under the heading,Authorization Information.

For additional information please visit the Authorize.Net knowledge base located at http://www.authorize.net/help. In addition a video tutorial on voids, refunds and credits can be viewed at http://www.authorize.net/videos.