I don't think the Ferengi are inherently bad as "merchant villains" just that, well... They weren't done well.
Fajo was just more like a the owner of a shady pawn shop with perhaps a touch of flamboyance and criminal activity.
The Ferengi it seems, at first, were just supposed to be something like anarchists that valued possessions and wealth above all else including civility. The execution....
I'd like to blame the make-up, the costuming or something like that but none of that really was it. It was portrayal.
In "EaF" Picard tells Zorn that he hopes the Ferengi will find Zorn "as tasty as they did their last business partner" or words to that effect. That's a lot to live up to and suggests a lot. Taken literally it could mean that the Ferengi devour people they can profit from and take the remaining assets. Taken figuratively pretty much means the Ferengi will come, strip you of anything valuable and then skip town leaving you in shambles.
There's a lot that could have been done.
Then "The Last Outpost" comes and the Ferengi are snarling little trolls squealing at the sound of thunder.
Doesn't impose me with much fear.