I am new to this forum, so please excuse me if i write anything inappropriate here. I want to take revenge someone who has basically spoiled my life. I did try to contact a black magic practitioner online. He asked for money and said that the work will be done, but nothing successful. I almost think he was a fake. Can someone show me the right direction or recommend me a good black magic practitioner. Thanks!

Instead of finding a practitioner, I would suggest crafting your own spell. One of the Saturn pentacles of Solomon would be great for using on a person like this, and they're not exceptionally difficult to make, and you don't have to be skilled at magic. You make it on the day and our of Saturn.

I wouldn't ever trust random online sites that promise to cast spells for you, not ones without legitimacy anyway. What are you trying to achieve with black magick? Simply to get them out of your life? Are you doing it purely on revenge? To hurt them? You are aware of the rule of 3, correct? Whatever you cast comes back to you times 3, so be careful with your intentions and be careful with what you cast out.

An it harm none, do what ye will. <- simple rule to follow (wiccan rede)

With that said, you can do what Raven said, create your own spell. You can do some research on the kinds of herbs, candles, oils, month, day, moon phase and position, etc. to help with your magick so it can be cast with it's fullest potential. There are also candles by Dorothy Morrison that I personally like to use when I can afford it (I ran into them visiting a friend at her shop, she was showing me some inexpensive blessed candles and I saw one that I needed by Dorothy) -- depending on what you're trying to achieve, she makes different candles for different purposes, all blessed and made under the full moon AND it come with a spell already written out for you to use if you'd like.

Anyway, just keep the rule of 3 in mind. Hopefully you figure out a solution to your problem.

beware of karmic retribution man ! being forgiver is better than be a revenger

The best thing to do is fix your life. That is more important than trying to hurt someone else. And remember that you only have two posts here. It is better to stay a while and let people get to know you first before asking for the best way to cause trouble for someone.

First. You need to specify what they did. Then you need to figure out why they did it. Telling us you want revenge doesn't help us. Or you. Did they physically hurt you? Did they cause some kind of trouble and won't stop? Did they steal from you? Hurt someone you love? There are other ways to solve this without black magick. Even without magick. You need to look through everything to find a solution that works.
Second. Magick takes time to work. It doesn't just happen when you want it to. Patience and keeping a level head is how you find solutions. But, if you do go the magick route, take heed of everything you've been told here. I hope you find a solution.