Concept:A proforma invoice is a preliminary or estimated bill sent before goods are finally supplied.
It is normally used for new or uncertain transactions.
Explanation:A proforma invoice is required when quoting for the supply of goods, as it shows the expected price.
It is also used when goods are sent on approval or when final prices are uncertain.
However, when a seller deals regularly with a customer, the terms of trade are already known and trusted.
In such a case, the seller may not need to send a proforma invoice before each transaction.
Therefore, a proforma invoice is not required when dealing regularly with a customer.
Answer:B. dealing regularly with a customer