It can be so frustrating to deal with people like that! What I have found usually works best with those types of people is to try to spin what you are saying in a way that benefits the person. So instead of saying that a hamster needs a large cage because it needs plenty of space to run around, you could say that having a large hamster cage is awesome because it will stay a lot cleaner with the same amount of effort. I work in a pet store and I've found that is the best way to convince people that little tiny "hamster" cages aren't going to work - they are too much effort to keep clean. If people think they are doing something for themselves they are usually more likely to go for it, and if it benefits the animal then it's good in the end.