Yes, it is. Tax authorities don’t really care about petty versions of it (like your example of a gardener), but they do care if you’re effectively a FTE being paid under the table.

(The gardener might also be filing 1099s or the equivalent without you knowing, but that doesn’t seem likely.)

woodruffw is right, you have to come to terms with the fact that a gov by default is made up of lowlifes. It actually gets worse, legally if you do not pay the guy who pulled weeds, you have to pay the tax on what his services would have been worth in the market. Well - it's true of Canada also :). Bonjour!