I read about this article and wondered as to why no mention is made about the fish diseases. I myself have gone through the agony of seeing my fish die infront of my eyes and was helpless.The petshop owners don't care much because to be very honest they more fish you buy,the more they profit.
I am providing a link to a very useful site which I feel every fish lover should read and keep some of the medicines handy.It helps if you do not waste time searching for these medicines from your neighbourhood medicine shop when your beloved fish are sick.
There are certain things the owners can do on a regular basis to keep their pets in good condition. 1)Water Quality(Check PH & Temperature at regular intervals) 2)Clean filters regularly(Do not use detergents) 3) Change 1/3rd water every fortnight. 4) Do not overfeed(Feed small quantities 3-4 times a day rather than a huge amount once) These simple steps will go a long way in keeping your fish happy. One last thing.The Goldfish look very pretty and are also easily available but I would advise first timers not to keep it.They need very special care!!