Exorbitant fees for insufficient fund transaction

There's one thing I don't understand about FNB . I transact with both my personal account and business account daily. Because of the nature of my business and my life in general I transact alot Sometimes monitoring my account between transactions is not always practical but a declined transaction due to insufficient funds i am charged 150.Is this standard procedure with all the banks and why so much.Also this happened twice this month and on the one instance I actually sufficient funds.