Assalaaamu `alaykum
This is how the Magicians earn their money. They are in contact with the shayaateen and through this- they do black magic etc and earn money. Allaah mentions how they have sold their Aakhirah for this dunya. It is indeed very strange and evil- How can a person not believe in Allaah after witnessing something from the unseen? Indeed, the worshippers of Shaytaan have sold their Aakhirah and indeed their punishment in the hereafter is great.
As for what you asked akhee:
- Using shaytaan to achieve wordly benefits: Many people firstly misunderstand the fact that Shaytaan does not know the unseen and also the shayaateen cannot do anything off by themselves- but it is indeed Allaah who does it. So, when supposedly the shayaateen give "Success"- then it should be known that this came from Allaah. Once this is established... we know that all success comes from Allaah and it is only befitting and makes sense to call upon Allaah alone. And remember that Shaytaan only knows what Allaah has allowed him to know, and he may not necessarily know the mysteries of the unseen.
- Selling your soul to Shaytaan: Know my brother than when a person starts to seek aid from Shaytaan- then this person has apostated. Thus, the magicians are all apostates as mentioned by the Sharee`ah of Allaah. Whoever turns towards shaytaan has left the pale of Islaam. And it is not worth leaving the religion of Allaah for the sake of becoming rich or finding the cure for AIDS or knowing the mysteries of the universe (all of which are not guaranteed in the first place). We know many stories of those who walked arrogantly in this world- committing shirk/kufr with Allaah- and we also know how Allaah destroyed them (Ex: Pharoah/Fir`aun).
Thus, none of this shaytaan worshipping is worth it. And yes, the person who seeks aid from shaytaan is a shaytaan worshipper and has left the fold of Islaam. And also look into what the scholars write about how the evil magicians get closer to shaytaan in order to please them. We see how they not only commit shirk with Allaah, but they have to belittle Allaah. Like for ex: They have to write the Qur'aan with Menstrual blood, put pages of the Qur'aan on their slippers and walk on the toilet floor. They are commanded by the shayaateen to drink menstrual blood, commit incest, not wash themselves for months etc. The shayaateen humiliate these people to such extents before giving their aid to them. While Allaah, Subhaanah, gave us honour, pride, dignity through worshipping Him!
P.S Ni`mah: It will be nice of you to not speak rudely to your brother. I have edited your post. Remember, Allaah commanded Moses to speak to Pharoah with gentle speech (when calling Pharoah towards Allaah). If that applies to Moses, then you should know that you are no better than Moses nor is brother Islamyay worse than Pharoah. Thus, speak with gentle speech.