Of course it influences behavior. Higher stamp taxes increase the incentive to cheat. That is why estimating revenue increases from such changes is always a challenge: a lot hinges on assumptions about the behavior of consumers and others. So what? Every business and every gubmint agency out there has the same challenges.
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It's not a challenge for politicians, they don't estimate the tax increases will lead to cheating, that's why everytime they raise the tax they get surprised by the "below expected revenue". Get it? D'uh.

It's like democrats and higher taxes, figuring everyone will just sit there and take it without any change. That's your static scoring. It's a little game hayseeds play because they want to believe it, and you're right, it has been happening for years, i don't understand why everyone has to go on pretending. It's stupid.