it's always good when they say "I don't have a net big enough for any of the fishes".. Sad part is I bet that pacu is going to be euthenized at some point most probably by the seller.
I guess that is what will happen at the local hopsital tank fairly soon. Except that the situation will be resolved somehow by the fish dying and the stupid idiot who stocks these tanks getting a few new baby pacus among other fish.
There's no excuse for not knowing the adult size of these fish ( among other things) if one has internet access. For the people who don't, they may have been misinformed by some other source.