The difference between plumber is recurring service. That being said, we have a bunch of customers that pay late. By late I mean, we do the spring cleanup in march and start mowing in may. Then we do fall cleanup in october and by december, they start calling saying: " I know I owe you a bunch of money. I will get you a check when I am back from florida."
Most people would say, you are crazy. They have a financial formula for this called Accounts receivable turnover. http://en.wikipedia.org/wiki/Receivables_turnover_ratio
Every business is structured differently. I personally would rather have the money now rather than later, but I don't mind the guys working and getting the money in the winter so long as I am not completely broke. It seems as though no matter what happens, we can not get Accounts Receivable under $10k until the winter time.
Then we just send a pink invoice saying "Last bill before we apply for a mechanic's lien". They always pay then.
That being said, I bill monthly. If it has been 60 days we usually go out of our way to make sure we are not sending to the wrong email address and/or they are getting the invoices.
Some people think that is outright crazy. Some would say normal course of biz. Everyone has different levels and tolerances.