If people did not pay their debts year ago they used to throw them in jail, it does not work like that anymore.
Here are some ideas that you can use.
Check them out
Particularly before letting them build up a decent amount.
ABN Lookup will give you some necessary information and also a link to their ASIC record free.
A google search may help you too.
Show your payment terms.
Rather then use something like "30 days from the statement" use our point of sale software to print out "Due by the 28 Feb 2018". In my experience "30 days from the statement" is the start of an argument.
Send statements regularly.
If someone takes six months to send a bill, few will pay immediately. I had one client that let his debts go and finally, his daughter took charge and had the great experience of ringing up people almost two years later, one this date you brought .... and when can we expect payment? The answer she often got was "Huh?", "who are you?" and "Come again". Our software can be set to regularly warn you, send emails, SMS if you like and printed statements too.
Keep records
When a debt starts to drag out what I do is print the relevant statement or invoice on an A4 sheet and on the back of it write detailed notes of my communication with the other party including dates and times. I also staple related notes on this statement. Make sure when you call you have all the necessary details to refer too.
Do what you are supposed to do
If they cannot pay, it does not matter what you say or do, you will not get it. A lousy payment schedule is better than nothing. You may lose on credit card but it gives the other side a month to pay it. If so I recommend once you get the payment you move as far away as you can from them.
Hope this helps.