Re: black magic
Assalamu Alaykum,
I think when they say that you recite the Quls, the important part is that you recite while understanding the meaning so it comes as a supplication from the bottom of your heart. If the meaning is kept in mind, and the Qul is recited, then definitely, it should help insha'Allah. I have also heard that there're narrations that one should recite Surah Baqarah (and Al-i-Imran) as well although I have not verified this. Of course, when one recites, the meaning should be kept in mind. Nonetheless, when An-Nas and Al-Falaq are recited, that should definitely be done.
Supplications from God of course should be sought. And lastly, one should definitely take any 'worldly' actions they have to take. By worldly, I do not mean going to pirs etc, rather that if the business is declining, one also make an effort to understand the causes, do their business planning and then fight the circumstances. We've been asked to both ask God for help and then make an effort. If we 'assume' (or even know) that business is affected by magic and don't make an effort, chances are that even when the magic is gone, since there's no effort, the business might continue to fall. The same is true of all similar 'worldly' cases.
Of course, I am not saying that anyone is not doing that, I just included every thing for the sake of completeness of post.
Best Wishes