Most every Petland is a franchise. meaning each location has an owner, and uses the corporate name, as well as being able to get product through the parent company. This gives them much more leeway, good or bad, as far as how product is bought, kept and sold. The owner has a vested interest in the location, unlike other chains where the store manager does not, and can bounce any of the more serious problems or situations up to corporate.
The retail pet industry, as with many other industries, is often vastly different from the consumer end. The fish you buy as a pet and give a nice name if referred to as product by them, as is common in the industry. If you expected them to keep fish as you do as a pet it is quite likely many fish would more than triple in price. While this in no way condones poor aquatic practices on their end, it is the way the industry works.
Posting pictures or showing them pictures of the natural habitat of the fish proves nothing other than all the fish we keep are unsuitably kept. I happen to keep & breed New World cichlids, my tanks are not even close to the size of the Amazon or its tributaries.
Having an owner, he/she is looking for a monetary return. The owner's family being fed and perhaps kids going to college takes precedence over the lives of the product he/she sells. Explain to the owner that the poorly kept product is a potential monetary loss, as well as a poor representation of quality pet care. Something his business would probably like to be known for is quality, this equals return customers, more product sales, and an increase in his/her profit.
Mention that if the owner and this Petland does not offer quality, the shop down the road will, and will reap the benefits of their poor product care and poor representation of pet care in general. The store is not a fish keeping venture, they store and sell product. Poor storage equals product loss. Focus on this owners main concern; the dollar.