Two of them come to mind right off the top of my head.
First of all, the way the procedural fairness letter is written—the way it's worded—uses a lot of legalese. It's hard for people to understand it and to understand the tests they need to meet and what information they might need to provide to overcome it.
The second issue is that when you provide your mitigation plan, they always give you this piece of paper that they ask you to sign to say if you're planning to pay for the services yourself. That conveys to applicants that if they just promise to pay for it themselves, that's going to be enough. In fact, it's far from enough. It's barely worth the paper it's written on, because everybody knows it's unenforceable. I've never actually seen an officer give that simple declaration weight.
It's important for people to know they have to back up their statements with evidence, and that the evidence should ideally be Canadian evidence, because that's the expense we're talking about. It's not what it is in your country, but what it is actually here. What would you be given here, what are you likely to use, and what is the cost of that? Most people don't understand that.
If they are not represented, you see people put in mitigation plans that really are not very good, simply because they are shooting around in the dark.