It may seem like a simple concept, but more businesses are saying they have to adjust their financial calculator due to customers who don't pay what they owe.

Protecting your business banking while still promoting good customer service can be difficult in situations where clients aren't making good on past due balances. According to a Kauffman Foundation survey, after overall sales the second-biggest problem facing new companies is nonpayment of debts, a problem that's only increased over the last few years. That may explain why the National Federation of Independent Business' small business confidence index found a decrease in expected sales and a continued negative sentiment toward positive earning trends.

"The customers are just unable or unwilling to pay in a timely manner, said E.J. Reedy of the Kauffman Foundation, one of the two authors of the survey.

Last year Rocket Lawyer asked nearly one thousand small businesses and respondents said about 50 percent of them had to write off debts of some sort, but they also listed a couple financial tips and ways companies found effective in getting clients to pay up. One-quarter had success with email petitions for late payment, while 30 percent tried formal demand notices and just over one-third called up customers directly.

In order to get a positive response from payment requests, try a number of different methods when a simple letter doesn't yield results. Communications leader Pitney Bowes recommends offering payment incentives, meaning give customers some kind of reduction in balance or remove late fees in exchange for full payment of the outstanding amount. Rocket Lawyer also found just over half of all businesses use legal contracts and nearly one-third insist on a paper trail to protect their assets.

Cash flow is important to fledgling businesses, and when clients can't or won't pay, it can hamper a company's growth. Estimations on the overall capital amount of unpaid invoices small businesses are carrying on average aren't available, but Rocket Lawyer noted 43 percent of companies have waited more than 3 months on unpaid balances.

"Young firms are facing challenging financial conditions due to difficulty in receiving payments," said Robert E. Litan of the Kauffman Foundation's Research and Policy department. "The cost to our economy … is that young businesses are prevented from adequately investing in their companies to fund growth and create jobs."