A credit card statement credit is a reduction in liability, so I would think it's "income" of a sort.
But, I could also see it as a reduction in expense; for example, buying a plane ticket using a credit card with 3% "cash back" (that gets applied as a statement credit) is sort of like a rebate or a delayed discount to that same expense.
Is there any general consensus or "best practice" for how to account for such things? I could enter it as a negative expense, or as a special kind of income. But if it's as a negative expense, it raises another question, which is: what kind of expense should it be entered as (i.e. which expense account)?
(The example with a plane flight and one big lump sum is clear enough as a negative expense, but how about 1% back on all purchases gradually adding up and finally resulting in one big statement credit?)
If it's entered as income, won't this falsely alter my income/expenses reports from a tax perspective? (Since it's not really income. Or is it, legally?)
I'm new to double-entry accounting and this question is general rather than specific to a single tool, but I'm starting to use GnuCash so answers geared toward how to implement the solution in GnuCash are especially welcome.