Well, first and foremost, personal communication by one flesh and blood human being to another.
Maybe we got their address wrong. Maybe they are on vacation. Maybe they are in deep financial trouble. Whatever.
The owner of my billing service gives them a personal phone call and asks, "Is there a problem?"
If there is a problem, we try to work it out. If it's a case of true financial difficulties, we reduce the bill, set up a payment schedule or sometimes write it off altogether.
If it is actually a case where you get a jerk, you let the collections process go to it's conclusion and they end up with a black mark on their credit rating.
Every once in a while, we get a sheepish phone call or even a personal visit to pay a bill that was "forgotten" or "misplaced". It seems that they lived with the black mark on their credit rating for a year or two untill they applied for credit and were denied because of it.
On the flip side, my billers told me last week of two cases with my accounts. We billed the insurance company $30 or so and they mailed us a check for $4,000. We mailed it back. On another account, the insurance company paid their share and advised us to bill the patient directly for the balance of......$9,000,000 (nine million dollars). Don't you just hate it when a computer key gets stuck. :-)
The bottom line is that mistakes happen all the time in billing matters and there is no subsitute for common sense and courtesy by all sides and, above all, humam beings talking to human beings and not simply relying on paper threats.