Set up Multiple Payment Channels
Make bill payment easier for customers. Besides cash & check, accept credit card payments and electronic funds transfer (EFT). Consider auto-pay. Add an online payment form to your website.
Automate Billing Processes
Provide your delivery drivers or service techs with a card swiper. They are typically free from your bank and allow the option to quick pay or offer discount for on-site payment.
Written procedures should be consistently applied to each customer. This avoids a situation where some customers to bend the rules. Conventional "net 30 days" will accommodate those that pay bills on a monthly basis. If a bill remains outstanding after 30 days, proceed with alternate measures of collection. Typically A/R gets grouped in 30-day buckets and labeled as 30, 60, or 90 days past due and business owners may use different collection methods. Letters & emails provide a trail of documentation, but may be easy to ignore. Phone calls are more personable and may yield a response or, at least, the negotiation of a payment plan.
Hiring Outside Assistance; it's time.
If a company struggles to pay you, they likely have a cash flow problem of their own. Make your terms clear up-front. When payment promises are broken, it may be time to hire a collection agency. By removing your team from the collections process, they are able to focus growing your business.