All of my invoices are due upon receipt. Nobody pays when they receive them. The large majority of my clients pay within 30 days sometime as a usual thing. I do have the occasional slow payer and when I get one I will send a statement at the beginning of the next month with a letter "reminding" them they need to pay this.
Even though I use the "due upon receipt" I know that the normal practice for almost all business is 30 days and I really don't start paying close attention to the aging schedule until I hit the 30 day mark. I also do most of my billing at the beginning of each month as a usual thing which is when statements will go out to people that didn't pay within the first 30 days.
If I don't get payment within 10 days of the statement I start with phone call, typically left after hours on their voice mail explaining I need payment and it is overdue. In almost all cases the phone call after hours gets me a check.
As a usual thing until I get to 45-50 days my collections efforts are soft. I try to not get out a stick unless it is becoming abundantly obvious they are not going to pay.
I have had a couple of hard cases where they didn't pay for months. In those cases I have my attorney send them a collections letter at 60 or 90 days depending on the circumstances and/or my history with the client. The less I know them or trust them the quicker they get the letter. I know this violates the "have a system and stick to it" philosophy, but it seems to work for me.
When I hit 60 days and my phone call and soft letter at the beginning of the previous month don't work I send a stern letter outlining what will come next, which is usually turning over their account to collections (my attorney) and/or other unspecified legal actions. Except for 2 cases in 5 years this step got me the payment. However one note of caution, if you send a letter like this and outline a process that will be followed, make sure you follow it! There is nothing that will embolden a deadbeat quicker than you issuing empty threats and not following through with exactly what you said you would do.
One thing I can tell you is not up for negotiation is once the letter arrives from the attorney the clock starts when I will file a law suit in court. I have the documents in my office and they are ready to roll if I don't have a check by the 30th day after the letter from the attorney goes out...no exceptions. I have never had to go this far to date, but have been fully prepared each time it started coming down to that option.
My philosophy is that if you aren't prepared to go all the way then don't have the attorney send them the letter, because if you do and then don't follow through the deadbeat will realize you aren't serious and may never pay or at least not for a very long time. I feel that I must make a believer out of them.
I agree with this statement a 110%, this is a critical step. I always ask for 50% up front and depending on the dollar amount in question a bill for another 30% at the half way point. I have a few clients I don't do this with any longer, but I have been doing business with them for years now and know them very well. In those cases I simply bill the entire invoice after I am finished. I will say that this upfront payment with intermittent billing will save you a TON of grief in collections procedures and/or any amount of legal effort. If people refuse to pay up front then they weren't a real client in my mind.