| Quote #4
"I've heard of his family," said Ron darkly. "They were some of the first to come back to our side after You-Know-Who disappeared. Said they'd been bewitched. My dad doesn't believe it. He says Malfoy's father didn't need an excuse to go over to the Dark Side." (6.262)
Somewhat conveniently, Malfoy's family blames their alliance on the "Dark Side" on being enchanted themselves. It's the kind of defense that's impossible to prove or disprove, and makes them suspect to people like Mr. Weasley, who believe that the Malfoys were already inclined to Darkness.
| Quote #5
"No – he wouldn't," she said. "I know he's not very nice, but he wouldn't try and steal something Dumbledore was keeping safe."
According to the conclusion of Book 1, Hermione is right: Snape isn't on the evil side here. While Snape acts really weird and suspicious throughout the book, giving Harry and Ron plenty of reasons not to trust him, ultimately Dumbledore himself defends the potions master. It would appear, then, that Hermione is right in her separation of Snape being "not very nice" from the idea of him working for the Dark Lord.
| Quote #6
"Can't have," Hagrid said, his voice shaking. "Can't nothing interfere with a broomstick except powerful Dark magic – no kid could do that to a Nimbus Two Thousand." (11.105)
Many factors combine here to emphasize how scary the enchantment of Harry's broomstick is. One, whatever did it is something that scares the large, confident Hagrid, who describes the situation with "his voice shaking." Two, broomsticks are complicated objects on their own and it would take some extremely "powerful Dark magic" to mess with them. Three, whatever did this is "no kid" but an adult with full-fledged magic powers.