Getting There, To me this post will have a wide range of answers, all of which are whatever is good and acceptable and works for the business model and experiences with non pays, etc...
We bill everything when complete with the exception of bat exclusion where we take deposits when booking. The rest is due upon completion and final invoice sent.
If I don't hear or see anything from someone after 2 weeks of completing larger work, I'm checkin in, just to be sure all is well and they received it.
This is a friendly nudge and not one using any language other than "just wanted to be sure you received the final paperwork and invoice?"
Factually I've had things go to spam including proposals due to filters on some email accounts, and so legitimately I want to know they got it.
The more outlay you have for equipment and time, the more concerned I'd be if you think you are going to get stiffed, however many larger contracts with towns, govts. commercial clients, etc... will all show you there are many ways that things must be setup sometimes and it may not be with a deposit, or maybe not amount you wanted up front due to their internal structure.
Can always walk away, but knock on wood, the only folks so far who ever tried to slip out on me were the cheapest jobs I had ever done, early on in my companies life and you can bet with the principal of the thing, I stayed on it, till that check came!
My best guidance, is you have to do what you know you need to do, to ensure you don't get overextended waiting on peoples good nature to pay you instead of some other bill first, or get a new set of tires, or family needs. Jobs that require less outlay I'm less punchy about, but the larger jobs require more discussion and meet and greet with companies and entities and the relationship to me is part of the glue that along with your contract for those, helps assure you get paid.
I will say I've waited nearly 70+ days to be paid out on some very large contracts because I was a sub, to a consultant who had to bill and be paid before paying me.
Assure in those broader scope jobs with other entities that you at least know up front what their best guess is on how long to pay.
I don't mind waiting as long as I don't feel someone forgot me!
Just my .02.
As was said and I agree, once job is done, payment is due, period. But most of ours until 30 days I don't get feeling bugged.