In cases where the taxing authority sues to recover taxes, should the burden of proof remain on the plaintiff as it would in any ordinary civil litigation?

Should it be on the taxpayer simply because the substantive dispute is one over taxes?

What should happen when the law establishes a presumption in favor of the taxpayer on a case-determinative legal issue?

Should the burden of proof for the entire case then shift to the taxing authorities, or should the taxing authorities have the burden only to proffer sufficient evidence to rebut the presumption?

As a practical matter, is there a difference between those two alternatives?