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.