I completely agree with listing the bala shark, pacu, and leporinus.
Petsmart markets the balas as beginner fish, when from much experience and loss of these fish, I know that they are neurotic messes!
As for leporinus, I haven’t seen them at petsmart in a while, but when they were sold there, I got three.
I wound up giving them away — they were monsters! However, now that I’m more aware of their aggression, I got one at the LFS, and now he’s 9 inches in a 60 gallon tank, with a 5.5” red belly piranha! He’s awesome! Just not for people who don’t know better.
For pacu, I strictly believe that they do not belong in aquarium care. Though some know how to care for them, most people see them as a $6 fish that looks like a piranha, and say “hey, that’s cool!” I was once that person when petsmart sold them (claiming they were slightly larger silver dollars). I wound up giving them away with the leporinus when they were the only things left.
Note that both the pacu and leporinus can wipe out entire tanks! From experience, I know that Pacu, the "vegetarian piranhas" ate whatever could or couldn't fit in their mouths, and the leporinus are highly territorial, and will kill anything that poses as competition.
I believe anything can be kept, with experience. Don't rely too much on what you are told. Do the research, commit to that fish, and DO IT RIGHT!!!
Non puffer freshwater discussion. Don't tell your puffers, they'll be jealous!