I would also say there are two kinds of clients, those who do pay and those who don't pay, and you're dealing with the ones who don't pay.
I'm taking a look here at paragraph 8.26, dealing with instalment remitters. It states: “...38 percent of total taxes owed by individuals. However, the Agency does not have more detailed information about these remitters that would allow it to understand the extent of the non-compliance and the reasons for it...”.
Why don't you understand 38% of your clientele?