I work at a local pet store and had the displeasure of trying to convince a woman she needed a bigger tank. The conversation started out as having 3 discus in a 100litre tank and one butterfly plec. A bad idea, but since she said they were all juveniles I said she had some time but NEEDS to upgrade the tank in the foreseeable future, if only for the fish's wellfare. Her husband came back to me maybe an hour later and started ranting and raving. I explained what she had said and what I had said in reply and explained the consequences to him. He revealed to me (by accident) that in fact, they were keeping 12 discus, 3 butterfly plecs, 2 common plecs and 8 malawis in a 100 litre tank. Originally, they came in because they were 'having an ammonia problem' and 'it sits at around 9 - 10 ppm' all the time.
No sh*t...
This happened yesterday and I forwarded his details (they wanted to order some filter parts originally and gave me their name, address and telephone number before the aforementioned conversation) on to my local authorities on animal welfare. I hope they get what they deserve.
Can't say I didn't try. I lost my rag with that pair in the end and asked them to leave the premises, barring them for life.