The most basic traits of Hufflepuff house are fairness, loyalty, and hard work. The sign of Cancer, the crab, assigned to anyone born between June 21 and July 22, matches many of its traits to those of the house of Helga Hufflepuff.
While a crab and a badger may seem like very different animals, and Cancer is a water sign, rather than an earth sign, the sign and the house seem to have far more traits in common than not. However, Cancer isn't a perfect match for every member of Hufflepuff house, perhaps the most diverse house at Hogwarts.
Typical - Loyal
Both Cancers and the Hufflepuff house are known for the loyalty of their members. It's one of the first traits the Sorting Hat mentions in its song before sorting Harry Potter and friends in Harry Potter and the Sorcerer's Stone. Hufflepuffs stand together in defense of Cedric Diggory when Harry is mysteriously picked as a fourth Triwizard Champion. They are also the house that stays most loyal to Hogwarts in the final battle, as only Gryffindor has more members represented in the Battle of Hogwarts. Many students who stayed behind to defend their school were like Cancers.
Not - Persuasive
Those born under the sign of Cancer are known for being particularly persuasive. Once they get a person's ear they are likely to keep it. Hufflepuffs, on the other hand, are the least underhanded of all the Hogwarts houses and the least likely to do everything they have to to get someone to believe their side of the story. Hufflepuffs are probably the most honest house, but that doesn't mean that everyone will believe them all the time, and that means they are less persuasive than those born under the sign of the crab.
Typical - Imaginative
Cancers are known for being very imaginative. While the most imaginative character in Harry Potter, Luna Lovegood, is a member of Ravenclaw house, Hufflepuff is perhaps the most accepting of imaginative people. Consider the variety of students accepted into the house, and the very original entrance to the common room itself. Knock on the right barrel and you gain entrance, knock on the wrong barrel and everyone will know because you get covered in vinegar. No regular passwords to memorize here. Cancer would certainly appreciate the humor and originality.
Not - Moody
Hufflepuff is often thought of as the happiest house. This is, of course, not true when Cedric is murdered, but that's a very specific circumstance. Slytherin is more likely to be recognized as a house for moody students, and Harry (particularly in his fifth year) makes the Gryffindor common room a very moody and brooding place to be.
Cancer may be moody, but that doesn't really match up with Hufflepuff overall. The coziest common room is too cheerful to be the best place to feel down and insecure, and self-critical.
Typical - Sympathetic
If you're looking for a shoulder to cry on try to find a Cancer or a Hufflepuff. Both are known for being very sympathetic. They'll take the time to listen to a person and their problems. They will also be the least likely friend to be judgemental about any and all conversations. If you want a good friend, pick a Hufflepuff, or a Cancer, or, if you have the option, someone who is both. Kindness comes in yellow and black.
Not - Pessimistic
Zacharias Smith may be moody, and pessimistic, and have an attitude, but he is an outlier in Hufflepuff house, which is partly why he gets so much attention from Harry Potter fans. Aside from Zacharias, Hufflepuff house, overall, is not a house that wallows and always believes in the worst. Cancer may be pessimistic overall, but Hufflepuffs are not. They work hard every year to earn house points despite an abysmal track record in winning the House Cup. Hufflepuff is a house for dreamers and optimists, not pessimists.
Typical - Insecure
Helga Hufflepuff agreed to "take the rest," when it came to the students she would teach, thus Hufflepuff house is often home to the most diverse students. This lack of definition, however, certainly leads to some Hufflepuff insecurity. Gryffindor is brave, Slytherin is ambitious, and Ravenclaw is smart. That doesn't mean that Hufflepuffs are none of those things, but it can certainly seem that way to a newly sorted eleven-year-old. Insecurity, as with Cancer, is common among Hufflepuffs.
Not - Suspicious
Hufflepuffs are the least likely Hogwarts house to be suspicious. Harry is suspicious, as he sneaks around with his invisibility cloak. Draco is suspicious as he sneaks around trying to mend the vanishing cabinet.
Draco and Harry match up with Cancer much more than Hufflepuffs do when it comes to acting suspicious or being suspicious of one another. Hufflepuffs like to believe in the best of everyone and, when they are angry, like with the "Potter Stinks" badges, they wear it on their sleeves.
Typical - Tenacious
Like any good Cancer, Hufflepuffs are tenacious. They are known as the hardworking house after all. They stick with each other, with Hogwarts, and to the projects and work they begin. Cancer and Hufflepuffs are probably most alike in how tenacious they are in any number of situations. If anyone is looking for effort and assistance a Cancer or a Hufflepuff is the person to have on a team.
Not - Manipulative
One of the least appealing traits in Cancer is their being manipulative. Trying to control a person or situation without seeming like they're trying to control a person or situation may be typical Cancer behavior, but it's not exactly a common Hufflepuff trait. If a Hufflepuff needs or wants something they are likely to ask for it outright or work hard to get it, not mess with the people around them to underhandedly succeed.