To buy off one's sins is only for human conscious but not for the soul.
Works like this, there is the human consciousness, the analytical mind and the unconscious mind. Yes we can fool the analytical mind, the conscious mind with charity events, with earthly activities, donations but all that comes from a place of fear based belief - remorse, heavy consciousness, clear consciousness terms are used for this but for the soul is nothing like that. Heaven and Hell reside in the very same location so to speak and we are the ones building our Have or our Hell.
Your idea "if somebody was genuinely wanting to "negate" their bad karma, would it be fruitless for them to do kind things?"
Karma means action and the negative karma or bad karma is an opportunity for the one who experience it to change, to transform the negative meaning throughout the action reflecting or manifesting in a positive way.
Giving money to charity clears a bit of consciousness but if what you put out doesn't come right away back, in the cycle of life it will, not this life? ok, in the next life experience... from here the idea of "transgenerational trauma"
Many individuals attached to karma a bad rep but it is nothing bad or something to fear.
Do good with open heart, good things will come to you.
Do bad things with a heavy conscious, more negative energy is attracted.
Looking a bit into conspiracy theories, there are (allegedly) individuals who want to live forever, some are afraid of the "hell" they have created for themselves and prolong their"human" experience through any means necessary, genetics and magic being a popular method....
Some cultures have a belief in which an individual consumes another individual's sins (called a sin eater), the christianity uses the absolution of all sins but all that are not for the soul but for the ego, for the flesh, bones and stupidity because, according to the very same christian belief the lord Jesus Christ sacrificed on that cross and for our absolution, he paid for our sins.
The soul's perspective is a bit more fun and less dramatic.
For the soul there is no sin, there is experience.
Dark night of the Soul is infact the Dark night of the Ego.
The soul does not suffer, does not cry, doesn't get wounded, cracked, splintered, shattered.... The soul is immortal, it is energy emanated from the Source of All There Is with the purpose of experiencing.
Yes for the human is a good idea to have and experience fear based beliefs because the negative experiences adds diversity, adds a whole new range of experiences which cannot be experienced if there was only "love and light".
Of course negative karma must have a bad rep because it serve the purpose of painting life experience in so many colors.
I know there is an universe where fear based beliefs don't exist or don't manifest like they do in this universe and if you have a little bit of curiosity and try to imagine such a life it is plain boring, evolution is linear, no reset button.
Karma is a tool, an opportunity, a reflection of the energy we emanate. It is like a mirror which when you throw a punch, you get a punch... when you smile, the mirror will have to smile back to you... (Bashar's analogy with the mirror is cool)
Again, dear old universe doesn't say "No"... never.
Soul agreements are also important. No karmic stuff in there.
"Under Divine Grace for the greatest good of All" that is also bypassing "karmic retribution" when some healers send energy to another individual.
I've typed a lot of nothing, sorry about that. It could of been less...