For a small business, that's often pretty hard to define. How much is your first marketing hire worth? Depends on how much business they bring in and how much they can get done before you need the second one. You can't identify in advance what marketing work is to be done and how important it will be - that's what you need the marketing hire for!

I'm not saying it's impossible to comply with salary disclosure, but it's harder than people think to make the disclosure "real".