When I went to petco for my first betta, an employee saw me browsing and approached me with one of those .5g marina squares. She said I could keep one male or 2 females it in and I'd only need to change the water every 2 weeks. I pointed to the 2.5 gallon in my cart and said that was for ONE fish, and she looked at me like I was crazy <.< "What?! They don't need heaters, just keep the bowl in the sun!" ....I just walked away.
I've also heard "You can keep red-eared sliders in a cage as long as theres a little dish of water."
I also HATE how they don't sell rats in pairs. They're pretty much tied with betta as my 2nd favorite pet (I'm a crazy cat lady). Very VERY rarely are they happy alone. It kills me that my boy Max has no playmates but he cannot stand other rats. He's a mush with people and spends alot of his day outside of the cage, but put another rat in his sight and he turns into a tasmanian devil. I've never seen anything like him lol