In the early days of my business, when we were more of a service company than a software company, I read this quote and it informed everything that we did:

>>> Nothing depreciates faster than the value of a service rendered. <<<

Always get paid in advance. We always had more customers than we could service, so we only worked on stuff that was already paid for. Customers became their own bill-collector when they were trained from contract signing that is how things work. Terms like "2/10 Net 30" will never make your life easier than simply getting paid first.