I have a good system with sae, although I provide a second class stamp! nearly all pay within 7 days.
the ones that are in pay on the day!
I offer online payment and more are choosing this also.
I have 400 a month that is done at the end of the week over 2 days that I collect. but this is all literally on my doorstep, and this helps with cash flow and its all CASH !...
I do have a handfull of bad payers , but rather than dump them I do them every few months on a sat morning!