Lets start by me asking what type of fish tank you have them in, and if you are buying them from extremely overcrowded chainstore fish tanks.
Well, it's a decent size tank (maybe two foot by one foot) for one or two goldfish. Yes, they usually come from the overcrowded fish tanks.
And another thing, why do the clerks put the fish in a little plastic baggy when you buy it? Are they too cheap to get little plastic containers? I'm always afraid the bag is going to fall inbetween the seats or through a crevice on the ride home. . .
Go to a decent fish store and do not get your fish from the overcrowded tanks. Feed twice daily, small amounts of food, goldfish do not require a heater, and would prefer a chiller if anything because they come from cooler water areas. They also produce a large amount of ammonia, much more then other fish, so clean and change the water once a week.
Yes, all fish stores are to cheap to buy plastic containers for the fish so they must use they bags... LOL
Most of the time, the markup on fish is around 3 times what they pay for them plus shipping and handling charges.