Providing a product or service for a customer, if delivered to the terms of your agreement, earns you the right to be paid & paid on time. If a customer is slow paying, there is normally a reason. Did you meet all terms of the agreement?  Deliver on time? Was the product/service sub-standard?  Was the payment period agreed upon & fair?  Do the terms of your agreement require a meeting to review & update? If all is in order, then it sounds like the customer is not able to effectively manage their business. I would consider taking them off your "A" list and making an effort to find "valuable" customers. Good customers also pay in a timely manner, without the requirement of multiple calls/emails to collect.  If you decide to keep them as customers, I would increase their prices to compensate you for the time required to collect payment. Good luck!!