The important thing to keep in mind is that billing mistakes are not uncommon and can be reduced significantly if properly managed. If you don't have an efficient method of verifying accuracy in place today, consider putting one in place soon. This isn't the way to maximize profitability, however. Most businesses are faced with borrowing money on an occasional basis. This is especially true during tight times and during periods of expansion.
Some businesses take on too much debt and the interest load is simply too large.
It is important for a business to pay down debt whenever possible to avoid the difficulties that come with servicing it. During more profitable times, use at least a portion of profits to pay down debt. Obviously, reductions in debt result in a direct impact on the bottom line through a reduction in interest expense. Whenever possible, pay down the principal of your outstanding loans. This will not only reduce interest expense, it will free up room in your operating line for future emergency needs as well.