the pet stores around my home are just terrible-I actually had to go to a neighbouring city to get good fish (eg ones that wern't sickly and stuff)
the minnows were big, but that store seems not to be very good with fish
Goldfish are a very hit or miss thing (eg the stores rarely have healthy ones)
its very common to see many unhealthy ones, dead ones, diseased ones, etc
thus they can sell them for 17 cents and no one really cares
the minnows seemed to be from a bad batch-though the mosquito fish I got with them is fine, oddly.
tropical fish are easy to get - I mean they tend to care for fish if your gonna spend like 10-20 dollars each on them.
my tank is 33 gallons, and temporarily has more fish then it normally does (but this is not for long) all the other fish seem fine, I guess that was just a bad batch.