Most Laws have come into place due to the stupidity and lack of savy (common sense) people have
yep and unfortunatly it goes both ways where stupiity is concerned.
easy example - piranha bans in the U.S.
Some places set bans since the fish could possiably bred and become established. And be a problem.
Some set bans when there was no such risk just because of the name piranha.
Some set or proposed bans because some idiot release a pacu and the news decided it was a "man eating piranha" to grab some rateings

the RSPCA should follow up these contracts and do regular checks, if the fish isn't being looked after the way it should be the person should be tryed and fined in a court of law under the animal cruelty act, the money from the fines should be used to house the fish, this way the fish will be looked after and we would have more public aquariums to help educate people about fish and reduce the amount of fish not being looked after properly!!!!

Not sure how it works elsewhere but in the U.S. that would be more of a mess then anything.
Someone would be responsiable for (aspca or humane society here) doing it. Likely there would be permits and fees to cover the costs.
Taxes would raise to cover part of the costs - next government budget fix would be to cut the service ,raise permit fees and make thinks 10 times more complicated then it started

on the flip side
Theres the argument thats been ongoing in several countries for years thats always over looked.
The fish feel pain and sufering or don't argument.
Right now - all the "official" results say no. With no sense of pain or suffering , is there a way to be cruel (law wise) ?
As fish keepers most of us have the tendancy to want to jump in and say something like of course fish feel pain.
But before you jump on that bandwagon remember In the U.K. , the U.S. and some other countries - if scientists and law makers would have agreed fish feel pain and suffer. Keeping of fish of any kind and sport fishing would have been outlawed by animal rights advocates already.
So which side do you support?
Look at your tanks and think "I take care of my fish" .
So do you want to keep them still, have some idiots around but try to help them when you can?
Or are you so against too small of tanks , your willing to give up your tanks?
Personally I sell a lot of fish and keep a lot of fish. Due to personal choice I don't offer people "large" fish (like arapaimas and arowanas ) because I think it's senseless. At the same time you won't see me run a boycott against them either because past laws have show how species like that can turn into list like
Oscars, PACU, Silver Sharks, Giant Gourami, RED-Tailed catfish, Arowanas, Metynnis- silver Dollars??, Plecostomus,
Yes I seem to be anti new laws at times when people read my posts on forums. And some people think I worry to much some times, but look at some local laws in the last few years.
Pitbull ordiances - locally were propsed as a keeper needed a secure yard and extra home owners insurance for pitbull - the laws passed as "dangerous dog laws" which is most of all large dog species.
Kennel laws - to limit the # of dogs a person can have - good idea

, except now if a female has puppies,the owner can be ticketed - yes I know unwanted and stray dogs can be problems but anyone know what happens with no puppies?
Local "Large constrictor" (snake laws) were proposed to keep people from owning large "dangerous" boas and pythons - wording of that law makes owning 90% of snakes illegal and "technically" it's more illegal to own a harmless cornsnake then it is to own venomous snakes.
Local "Marsupial law" was proposed to stop people from buying kangaroos and others that get large. - What passed is all pouched animals - marsupial tree frogs , sugar gliders and more. For some reason I don't think people had an issue with tree frogs when the mess was proposed.
and we would have more public aquariums to help educate people about fish and reduce the amount of fish not being looked after properly!!!!
Sadly that doesn't seem to be a trend either (in the u.s. anyways) . Some people from my site got together for a zoo tour 2 weeks ago and they had a lot of new fish in quaranteen. Most of those fish came from other zoo's who were "perminately dismantleing" or "phaseing out all their freshwater".