Never PAY for coaching for anyone under diamond 3. There is a website lol-coaching.com, there you can find a list of a lot of coaches willing to help you out and work with you.
And coaching does actually help people, not everyone, but a lot of people can benefit with guidance. If you are finding yourself in a situation where most of the games you do really well (or at least you think you do) but you still manage to lose most of your games, you can definitely benefit from it. If you're only playing with bronze kids the majority of your games, you're not going to progress nearly as fast as if youre playing with and against plat and diamond players.
I alone have helped people get from silver to plat, or bronze to gold.