List the customer's name from the South region with a standard class ship mode and sales greater than the 88% of the average sales of all orders.
sales greater than the 88% of the average sales of all orders refers to Sales > avg(Sales) * 0.88; South region refers to south_superstore
SELECT DISTINCT T2.`Customer Name` FROM south_superstore AS T1 INNER JOIN people AS T2 ON T1.`Customer ID` = T2.`Customer ID` WHERE T2.Region = 'South' AND T1.`Ship Mode` = 'Standard Class' AND 100 * T1.Sales / ( SELECT AVG(Sales) FROM south_superstore ) > 88