Someone told me that any kind of voodoo will eventually backfire on you, and she told me how she did the voodoo spell with the jamjar which causes a specific person to have good thoughts toward you, but I will summarise and say there was a LOT of backlash, so does voodoo in general bare bad consequences, eventually?
What if you completely refuse to acknowledge the concept of karmic payback or whatever, if you attempt voodoo or any spells with a lack of belief it won't work, so what if you don't believe it can backfire?
If you believe something bad will happen to you or fear it when casting any magick then you will manifest your own concerns.
The only other backlash you can get from casting, is casting the wrong spell for the situation. You need to have understanding and experience of life in general, know the nature people, and make good choices. For instance, if someone is lying, and you cast a truth spell, and the lies were made to protect someone from getting hurt, then perhaps you should not have meddled to begin with. There is great responsibility in magick. Frivolous choices create more problems. You need to be able to judge when to cast and what to cast correctly. And that good judgement comes with life experience.
By the way vodun/voodoo is a religion not a craft. Hoodoo is the practice of folk magick that most vodun priests and priestesses practice. Just calling it "voodoo" shows both your friend and your ignorance in the field (no offense).
personally read into voodoo to see if it's right for you [as raven said, voodoo is the religion hoodoo is the practice] there is nothing wrong with voodoo, as there's nothing wrong with most forms of magic. where voodoo looses it for me is the use of animal bones and other types of things that i morally don't wanna deal with. [scratch that, bones are fine, animal sacrifices aren't, but that's kinda rare]
what your friend was referring to with the jam jar is a honey jar spell, basically you place a bunch of similar items in a jar to attract things [love, luck, wealth] they're highly effective every times i've made one. there is nothing evil about it unless your intent is such. if you don't believe in karma, then that's fine. personally i believed in it when i first started out but i've seen so many good things happen to bad people and vise versa i find it hard to justify myself. however, just because you don't believe in karma doesn't mean bad things won't happen if you curse someone, or meddle like raven said. the best intentions could end badly.
to build on the above example. let's say your friend is rather quiet around you and you feel somethings bothering her, so you ask her and she says she doesn't want to talk about it. you feel things would be better in the open, because bottled up they will just fester. so you cast a truth spell upon her, and that's when you find out she slept with your boyfriend [as an extreme example] now she's said it, but you loose trust in her, and depending on how good you are with forgiving that sort of thing, break up with your boyfriend and probably stop talking to her as well. truth spells is another one that can fall under 'grey magic'. while magic has no colour, it can be categorized by people a lot.
white = good
black = bad
grey = both
grey is when good intentions imposes ones will on another. this is why magic needs to be thought about long and hard before doing anything. typically magic comes down to the casters intent, but in situations where the intent is good, but the casting involves doing so upon another unwillingly, it leaves wiggle room for it to backfire. this isn't necessarily karma, but just negative results. like adding too much soda to vinegar, a little will make it foam up, a lot will make it overflow and spill everywhere.