I don't think they are - I think it's just a misunderstanding of phrasing maybe? I interpret "I should have paid more" as I should be compelled to pay more, no

I don't think they are - I think it's just a misunderstanding of phrasing maybe? I interpret "I should have paid more" as I should be compelled to pay more, not "I wish I could pay more". The distinction being they'd rather not pay additional tax, but they probably should have to. I think the language is just somewhat ambiguous (specifically the word 'should').