Not based in the US, but due to general tax law complexities, tax authorities definitely negotiate over the specifics and interpretations of laws, as well as th

Not based in the US, but due to general tax law complexities, tax authorities definitely negotiate over the specifics and interpretations of laws, as well as the amount payable (source: personal experience). Having a good lawyer from an established firm with an excellent name helps a lot as well. If you're small fish, don't be surprised if civil tax servants try to bullshit you on the law. Be willing to fight (and prove them wrong), or be eaten. On one particular case I'm aware of (friend of a friend), a seven figure tax sum was payable. They eventually settled everything for $25k because they weren't sure of their case.