Here, I’ll mention some traits that all Hufflepuffs share. I think that what makes a Hufflepuff a Hufflepuff is so much more than being nice and fair to people. They can be amazing people, and are worthy of being called ‘decent people’.
Hufflepuffs are able to be fair even towards those they dislike: I think that Hufflepuffs would almost never be unfair to someone just because they don’t like them. A Hufflepuff teacher would give a student a fair grade, even if that student is a troublemaker or a little rude. A Hufflepuff judge would be the perfect judge, because they would be impartial. On the other hand, even if they act unfairly to someone, they would try to make up to that person, or at least apologize.
Hufflepuffs love to help: I don’t think that a Hufflepuff would just sit and relax, if their friends are in trouble. Didn’t they help Harry, Order of the Phoenix and the Dumbledore’s army, during the Battle of Hogwarts, on May 1998? Also, if you need help with something, I think that a Hufflepuff would almost never say ‘no’ to you. They love to help people and to be of use. As we know, they are known as hardworking, nice and patient people. Also, remember when Harry stayed in the Sirius’s house during the 1995 summer. That summer, didn’t Tonks insist many times on helping Molly with her housework, even though she kept falling on the ground, because of her clumsiness? Also, Cedric Diggory is the perfect example, and I think that many Hufflepuffs are not to his level at all, but I take him as an example no matter. He helped Victor Krum in the ‘Triwizard Tournament’, when he was injured, even though Victor tortured him (Well, Victor Krum was under an Imperius Curse, after all!).
Hufflepuffs love food: Another thing, which I think all Hufflepuffs have in common, is their love for food. After all, their house is near the kitchen. I think that Hufflepuffs have a genuine love for food, and that a perfect evening for a Hufflepuff would be to stay in front of the fireplace eating their favorite foods, including of course a hot chocolate mug, after a long day of hard work.
Hufflepuffs will almost never tell your secret: I think a Hufflepuff would respect someone’s privacy. They wouldn’t gossip about a friend’s private issues. Also, there aren’t any traitors among Hufflepuffs. That’s another trait they have in common. But, I think there is an exception. They would always keep a secret, unless keeping that secret means endangering someone. For example, if their friend is a murderer, then they might keep that as a secret, unless someone is about to be imprisoned or get executed for that particular murder.
Hufflepuffs are practical people: Hufflepuffs are probably the most practical people in Hogwarts. I think that most likely, they aren’t type of people to sit down and discuss theoretical problems, but that they are type of people that like to solve problems of practical nature. For example, the one who invented the Self-Soaping Dishcloth was a Hufflepuff, which is a very useful and time-saving thing to have.