As I understand it, the Ferengi were set up at the beginning of TNG to be the next "big bad" of the galaxy, and their capabilities are described as being equal to the Enterprise's. That being said, they do so much to violate intergalactic law, not to mention irritate and antagonize everyone they encounter, that it seems stunning that no one has launched a photon torpedo down their throats out of pure frustration.
In one episode they attempt to assassinate a Federation captain using a stolen Federation ship, in another they attack two Federation ships during a routine training exercise just because they thought there might be something they could steal. They routinely threaten, bribe, and falsely accuse other races and individuals, regardless of their power or rank. They've kidnapped Betazoid royalty and Federation personnel, they've deliberately tried to destroy property they couldn't purchase, and they don't even seem to apologize for (or even deny!) most of their actions.
I've only seen TNG, not DS9 or Voyager, but does anyone ever comment on why the Ferengi haven't been the subjects of a Klingon or Romulan genocide, or how they seem to commit so many acts of war without ever actually going to war? Even if we assume they are as powerful as the Federation (which the shows seem to walk back a little after their first introduction), they've committed plenty of offenses which would justify a Federation response, let alone a response from one of the more militant galactic powers.