Ask HN: SaaS Startups- What solutions work to ensure payment from customers?

- We bill via invoice (net 30), even though we have 1 year contracts in place, many of our customers are very untimely in paying us, sometimes >1 month late, despite many follow up emails. These customers are large, we're not worried that they don't have cash flow.

- Have you had any experience with outsourcing collections / some sort of service or product, and to what degree of success have you found?

- Is it common to have a hard time collecting on cash post sale?