The irony is that the honest users won't expend a lot of effort evading, while the scummier users will (and have a much easier time of it, since they've done it

The irony is that the honest users won't expend a lot of effort evading, while the scummier users will (and have a much easier time of it, since they've done it 100 times before). In this way anti-fraud filters sometimes act as pro-fraud filters: False positives kill honest use, and dishonest use finds a way.