Trusting Does Not Mean Naïve
Story: The Parkinson Family has abducted Harry from the Dursleys in the hopes of gaining his help against Voldemort… It goes badly.
Lord Malcolm Parkinson had finally completed his long tale and plea for help. He first profusely apologized for essentially breaking into Number Four and spiriting him from the Dursleys without his knowledge in the middle of the night.
Then, he'd explained to Harry that the Parkinson family's commitment to neutrality in the previous rise of You-Know-Who had left them with few allies in pureblooded society when Malfoy began to amass power after families like the Potters, Bones and Longbottoms were all but wiped out.
He told Harry how he and his wife Esmeralda had known Harry's parents and while not as closes as Sirius or the Longbottoms had cared a great deal for them.
How, when Pansy started Hogwarts they instructed her to get sorted into Slytherin, try to get into Draco Malfoy's good graces but otherwise keep a low profile. They even went so far as to hide her surprising beauty behind a glamour and mild use of notice-me-not charms just to protect her from Lucius' wrath.
Then he all but begged Harry's help in exchange for helping to train him in ways Dumbledore wouldn't and teaching him of his considerable role in Pureblood society offering enough of his family history along the way to tantalize him before the room finally fell silent.
Harry looked around the small breakfast nook. He look from Mr. to Mrs. Parkinson's calm expressions each had a hint of worry in their eyes. Harry then turned to the frankly stunning face of Pansy Parkinson; his brain had a hard time reconciling this pretty-face with the harpy in training that had hung onto Draco like a pilot fish.
The silence threatened to stretch out even further until Harry cleared his throat quietly and meekly asked for the tea. Mrs. Parkinson handed him the pot and he let the spout hover over his cup for just a moment before he moved.
Several things happened so fast and in such quick succession that the kitchen was plunged immediately into chaos. Harry swung the tea pot with all his might into the face of Esmeralda. She shrieked in agony as shards of pottery and scalding hot tea shredded her flesh and she tumbled from her chair, clutching her face and howling.
In the next half-second, Harry then surged to his feet, dumping the table into Malcolm; the man was still too stunned to even put together thoughts of action so he too was thrown to the floor.
Pansy had only really started to process what had happened and as she surged to her feet Harry took her throat in an iron grip, he then took a step back and pulled her in front of her as a human shield. He then took a fork that he'd palmed as he upturned the table and jabbed it hard against her throat.
Parkinson rose to his feet in a fury and started to level his wand. Harry then moved Pansy into the line of fire and yelled out, "Don't! Because I swear if you fire a spell at me two things will happen; first you'll hit this cow you call a daughter. Second, I'll jam this fork as hard as I can into her neck and attempt to tear it out as much as I can as I pull it out."
He ignored Pansy's whimper and continued on, "Do you take me for a fool? You kidnap me. You slur the only people who've ever treated me as anything other than a leper. Then you throw out my parents' names and my family history like party favors and you expect me to believe you? You expect me to believe this bitch here, who's called one of my only friends a Mudblood on numerous occasions, not to mention taunted the son of one of you 'purported' close friends too many times to count has only been doing it to avoid the wrath of Voldemort's sycophants?"
Parkinson growled, "Potter-"
Harry jerked Pansy causing her sob, "SHUT IT! Call one of your elves, and have that elf take me to aurors! NOW!" Harry's eyes narrowed as his face hardened, "Unless you want your wife to continue to writhe in pain while your only daughter bleeds out instead of you taking them to either your Master or St. Mungo's. I don't believe your sob story and I don't care to help you garner favor with Malfoy or Voldemort!"
There was a tense moment between the two before Parkinson called an elf and instructed it to take him to Ministry while he took his wife to St. Mungo's. The last thing Harry heard from the Parkinsons was them damning him.
He thought very little of it until a few months later when he heard that Voldemort had killed the Parkinsons when Malcolm refused the mark. After that, he thought about that day for the rest of his life.
Post Note: I know it's a required premise for Harry to believe these grey families if for no other reason than to forward the story but I just don't see how this situation can't be considered the just as likely outcome of the situation.