Who is really to blame for this!?! Fish shops/pet stores, if they would give a little of healthy information once in a while fish wouldnt be mistreated, but no, the majority of LFS will sell you a goldfish or other large fish, or any fish for that matter with no questions asked.
I think both are to blame to be honest. Fish stores
do state fish sizes on the cards saying what the fish are, but the cards are always tiny, and the info on size is even smaller in text so people simply don't look at it.
Thing is if fish stores and shops put up a sign or clear info as to what goldfish actually require in terms of a very large tank and a good external filter plus the long lifespan of well kept goldies, then people would simply think "sod that" and not bother to buy one, which would lose them business.
My LFS does have a sign on the goldfish tanks that states they must not be kept in anything under 80L . While 80L is still vastly too small in every sense of the word, it is a step in the right dierction I think.
On the other foot, buyers , wether they want the fish for something to look at/decorate ( a despicable reason IMO but it can't be helped ) or because they genuinely like them and want some interesting pets, should
research the fish they like the look of, what tank size and setup is required, and to set up the required tank properly
before buying.
Sadly it seems about 90% of the people you see buying fish in stores are impulse buyers replacing fish they lost because they didn't do the required research and caused deaths as the consequence.
I think perhaps it would be good for fish stores to put up a large notice entreating customers to research the fish and requirements
before buying to save a lot of hassle and have a healthy tank, perhap providing info leaflets on popular species such as goldfish, neon tetras, bettas, plecs ect for customers to take away and read before getting a fish . Basic info on tank setup and mainetence ( such as the importance of weekly water changes and monthly testing ) and a reccomendation list of books containing reliable information would be good to include too.
Even someone who only wants a tank for decoration, doesn't want a load of diseased or cramped and stunted fish so such a notice can only be a benefit.