Yes, it’s hard.
They were introduced to be annoying greedy little trolls. The kind of character you wish was wearing a red shirt.
By the time DS 9 came around and you saw Quark behind the bar, you knew that he was going to betray, trick, annoy, and wondered why no one else opened a bar and put him out of business.
As the seasons continued you found Rom was an ‘idiot’ and ‘Nog’ the kid you wouldn’t let your son play with. The writers had taken every ugly trait, packed it into the Ferrangi and put them out there as the universal scorn.
Then something changed.
An entire culture was built, using the Rules of Acquisition and becoming an example that Consumer Organisations could use in argument; “We are not on Feranganol, when you get a customer’s money, and don’t supply the product or live up to your guarantee.. you have to give it back.”
We began to realise Rom was not an idiot, he was a good engineer, and Nog became a Star Fleet Officer. Someone who could stand up during battle.
There was a depth to Quark, an intelligence, and he was all of one piece. He was not a coward, he could display real courage and strength when necessary.
We found ourselves liking the little troll.
We liked him for his honesty; if the Klingons had taken the station, he was ready, if the Dominion, he was ready for that too, for business was the focus. He didn’t shroud his greed for profit in distracting philosophy, Profit was the core of his being.
And it is nice to have a character, a set of characters, whom you can easily understand