Here are some helpful answers from HighRiskMerchantAccounts.co.uk underwriting department to help merchants reduce their chargebacks.

Cards that do not swipe properly
If the credit card terminal cannot read the card because of mag stripe issue. Your staff can manually key-in the card number and expiration date of the card. We strongly advise to make imprint of the card using a manual imprinter. The imprinted sales draft of the card must contain the bank approved sales data, including the cardholder's signature. Do not refuse to accept a card simply because the magnetic strip cannot be read because you will probably loose valuable sales from your customers.

Retrieval Request
A retrieval request is a request for a copy of a credit card receipt. Once a retrieval request letter is received either by mail or fax, provide a legible copy as soon as possible. Please note all credit card receipts must be maintained for 7 years from the date of each transaction.

Return Policies for all Merchants
To be considered proper disclosure, your return policy must be on your sales draft at the time of the sales and printed prominently in close proximity to the cardholder's signature. (e.g., No Refunds, All Sales Final)

Mail Order / Telephone Order Transactions
If you process MOTO transactions, be sure to use Address Verification Service (AVS) and request the customers CVV2 number that appears on the back of their card. AVS will only help but not prevent 100% all chargebacks, and it does not work outside America. but it will still help you reduce fraudulent transactions. Obtaining CVV2 numbers are the 3 digits on the back of each card is most important a plus watching your online sales for suspicious transactions such as large dollar sales, or rushed orders that are from countries that have a high degree of credit card fraud will help the online merchant reduce fraud transactions. All sales must be processed within 7 days of the date the authorization was received. If merchandise / services are not available within 7 days, obtain a new authorization code prior to processing.

Authorizations
Request an authorization on every credit card sale. Once an authorization attempt is declined, do not attempt another authorization. Ask for an alternative payment source. If you process a credit card sale that was declined, or previously declined, the cardholder's bank may initiate a charge back.

Debit Card Returns
If returned merchandise was purchased using a Debit Card, you have the option of providing the cardholder with cash or an in-store credit. Do not attempt to process Debit Card refunds electronically.