Hey guys!
I'm wondering if you know some tricks to be able to just target business owners or people able to take important decisions like high level executives because i want to offer some taxing services to them.
Thanks in advance.
You can start by testing job titles: (Demographics>Work>Job Titles [Search])
Behaviors > Job role > [Corporate executives / CEO / Founder / ...]
I would definitely also test interest targeting. Start with some CEO magazine for an example and then combine with suggested relevant interest to get bigger audience. CEOWORLD Magazine is only 85k... it's not scalable but it's probably highly relevant audience.

^ Very clever mate great share
Enter as many small business interests you can think of related to conferences they might attend, magazines they read, softwares they might use.... After that hit 'suggestions' and fb will give you more ideas so you no longer have to brainstorm.
I would try to split-test your settings with general niche-related topics. The answer might be somewhere in between. Also +1 to luckyluciano's post 