Include your warranty information, and your returns policy. Be as detailed as possible, to ensure potential buyers are comfortable with your policies.
Make it as easy as possible for people to purchase items from you, by having multiple payment methods. Common methods include PayPal, Bank Deposit, Money Order, Bank Check, C.O.D., etc. You should also include information on the number of days a buyer has to make payment.
Make sure you give the cost to post the item, as well as an estimate on delivery time. You will find more potential buyers if you make your items available for worldwide shipping. If you have multiple items for auction, offer discounts for repeat purchases.