Industry reports consistently state that around 80% of all retail staff fraud is conducted at the point of sales by till manipulation. Till manipulation fraud is the alteration of transactions on the till for the purpose of liberating cash or goods.
There are many classic methods that are used. Full details can be found here.
The aim of a refund fraud is to process a fake return of goods and to steal the money allegedly paid back to the (fake) customer. In most retail businesses, some employees will have the authority to process returns of the goods in certain circumstances.
In a real return of goods, the customer will want the money or a credit after returning the goods, so using real returns for this fraud may be difficult. A false return must be created, processed and the money taken.