That is the best way to get resolve, put it in writing, and go above the managers, they need to have the Coporate Offices know that not just one Petco, all in the chain needs a complete overhaul on Proper Fish Care!!
I go to my local Petco, and most fish are in ok conditions, but at times, and yes, I beleive it depends on the employees, and the time of day..or day of week, when your find more deplorable conditions. But it should not be that way, everyday of the week the fish should be in the best possible condition, starting with getting them out of those cups, and getting them into something else, like the divided tanks, or bigger cups, that should be brought to Corporate's attention too, they could easily order something bigger to house the bettas in for temporary status. or the ones that have been there longer, start moving them into bigger quarters, so that they won't have to endure the long stay..I know some say they've seen the same fish there for months, in thier local PetCo/Smart..they are all the same, and it is called animal/fish abuse, and it's wrong, and needs to change.