The problem with the Ferengi is that you can sense they were supposed to be menacing and mysterious, when in fact they were just kind of silly (even though they did manage to dupe the Enterprise's crew on a few occasions, if memory serves). Early TNG, people were all "wow, the Ferengi, no-one knows anything about 'em", but when you examine DS9 chronology, you have to wonder if the Enterprise simply didn't have access to space internet.
Actually they seem to know alot about them.
Captain's log, stardate 41386.4. We are in pursuit of a starship of Ferengi design.
They know what their ships look like.
RIKER: Anything on that design, Data?
DATA: Nothing specific, sir. As you know, Ferengi technology is estimated to be generally equal to our own.
They know their tech is roughly equivalent to the UFP.
RIKER: Which reports do not conflict?
DATA: That the Ferengi are, well, the best description may be traders.
PICARD: What kind of traders?
DATA: A comparison modern scholars have drawn from Earth history likens the Ferengi to the ocean-going Yankee traders of eighteenth and nineteenth century America, sir.
RIKER: From the history of my forebears. Yankee traders.
DATA: Who in this case sail the galaxy in search of mercantile and territorial opportunity.
RIKER: And are those scholars saying the Ferengi may not unlike us?
DATA: Hardly, sir. I believe this analogy refers to the worst quality of capitalists. The Ferengi are believed to conduct their affairs of commerce on the ancient principle caveat emptor. Let the buyer beware.
RIKER: Yankee traders. I like the sound of that.
DATA: Well, sir, I doubt they wear red, white and blue, or look anything like Uncle Sam.
They've a pretty good idea what Ferengi society is like.