(Guiltless in cent.) when I've taken a chair.
(Absence of all thing) asserting thing there.
(Not any human one) it is true.
(Sure of kw.) a small charge for you.
The answer is a song title. "Classic" refers to the song not, of course, this riddle. The song is one of the best known I could think of. Most of the clues are not cryptic (in the cryptic crossword sense) yet the cryptic mindset is important to arrive at the solution.
There are no intentional acrostics here. I just noticed that the first letters spell "snag" backwards. This has nothing to do with the solution.
Perhaps to get it, you should proceed piece-wise and Chinese fashion.
Change your perspective. Think vertically. I have a feeling the answer and its opposite will come to you suddenly.