Sometimes writing a letter or saying something to a petshop can help. For instance, I asked a shop to correct the temperature recommendations for bettas, and they did, happily. Sadly, some shops also pull out a load of rubbish about how their tiny tanks and lack of heat are certified by "experts" (I suspect they are marketing experts, rather than fish experts).
Thankfully, one of my local shops has started selling a 9 litre betta kit with a heater, gentle filter and a lid. It's still not as big as I'd like, but it's so much better than those kits that treat fish as decorations, not living creatures.
One of the things that bothers me most is that they sell a 19.5 litre starter kit, which is nice, but if you are a member of the store you get two free COMETS with it. They don't seem to realise that they are giving people fish, that, under proper conditions, will grow more than a foot long and live for 20 years. If only you got two free guppies or something. I don't like guppies in less than 10 gallons (40 litres), but they'll do a lot better than the goldies. :(
Sadly, Backlash, trying to get governments, whether local or national, to start off law reforms regarding animals is far more difficult and less effective than campaigning with local stores, for several reasons.
Firstly, most people don't like "nanny-state" laws that infringe on their autonomy to such a degree.
Secondly, you've got to make the governments care. When they are legislating about wars, refugees, old age care, educational reforms etc, they aren't going to make time to make laws regarding what they see as "just a fish". Even societies like the RSPCA won't help fish because of bigger problems - the government sure won't.
Thirdly, explaining these things to shops in terms of profit as well as animal cruelty can be effective - what's more effective is targeting the customers.
Fourthly, if we don't have a big enough movement to affect shops, we certainly don't have a big enough movement to affect government. We'd just be written off as a loony, hippy fringe group.
The only solution is educating people, one fish at a time. :( At least it makes a difference to the life of that fish. :)