engine - 5:15 pm on Aug 12, 2011 (gmt 0)
Welcome to WebmasterWorld.
I don't know if these earlier threads give you any pointers.
eCommerce: Improving Sales Conversions When Price Isn't Always The Lowest [webmasterworld.com]
eCommerce: When Traffic is Up and Sales are Down, Where Do You Look First? [webmasterworld.com]