One of the typical bookkeeper frauds I see more frequently consists of applying for company credit cards using solicitations received in the mail.
There should be a separation of responsibilities when it comes to mail for small businesses. The person that pays the bills should be different from the person that receives the customer payments which should also be different from the person that receives the mail.
My advice is for small business owners to get a post office box or a get a mailbox where only they have access to the mail. After going through the mail, destroy unnecessary solicitations by shredding them and then distributing the mail.
Bookkeepers will apply for the company credit card and if they fit the "fraud triangle" will charge personal expenses and pay the bill from company funds. Most times because bookkeepers are trusted employees, business owner will never question the validity of the charges or even review the statements. These frauds can cost the business owner hundreds of thousands of dollars before being discovered.
These types of frauds can go unnoticed for many months and even years. Business owners should always have a level of professional skepticism of their employees and operations and never place a level of undoubted trust in their employees.