In *Goblet of Fire*, Harry's close friends, and even best friend (Ronald Weasley), suspect him of sneakily getting past Dumbledore's age line and putting his name in the cup, and even when Harry *repeatedly* clarifies the truth, petty jealousy seems to trump their 4 year long best-friendship and everything Ron knows about Harry, such that he believes Harry is now *lying* about not having anything to do with the name being put in the cup.

I can understand why the majority of people think he tricked the cup, but his best friend, even after repeatedly clarifying?

>Harry turned to Ron and Hermione; beyond them, he saw the
long Gryffindor table all watching him, openmouthed.  
“I didn’t put my name in,” Harry said blankly. “You know I
didn’t.”  
Both of them stared just as blankly back.  
<sub>—*Goblet of Fire*, Chapter 17, The Four Champions</sub>  
>
>“So,” he said, when Harry had finally removed the banner and
thrown it into a corner. “Congratulations.”  
“What d’you mean, congratulations?” said Harry, staring at
Ron. There was definitely something wrong with the way Ron was
smiling: It was more like a grimace.  
“Well . . . no one else got across the Age Line,” said Ron. “Not
even Fred and George. What did you use — the Invisibility
Cloak?”  
“The Invisibility Cloak wouldn’t have got me over that line,” said
Harry slowly.  
“Oh right,” said Ron. “I thought you might’ve told me if it was
the cloak . . . because it would’ve covered both of us, wouldn’t it?
But you found another way, did you?”  
“Listen,” said Harry, “I didn’t put my name in that goblet.
Someone else must’ve done it.”  
Ron raised his eyebrows.  
“What would they do that for?”  
“I dunno,” said Harry. He felt it would sound very melodramatic
to say, “To kill me.”  
Ron’s eyebrows rose so high that they were in danger of disappearing
into his hair.  
“**It’s okay, you know, you can tell me the truth**,” he said. “If you
don’t want everyone else to know, fine, but I don’t know why you’re
bothering to lie, you didn’t get into trouble for it, did you? That
friend of the Fat Lady’s, that Violet, she’s already told us all Dumbledore’s
letting you enter. A thousand Galleons prize money, eh?  
And you don’t have to do end-of-year tests either. . . .”  
“I didn’t put my name in that goblet!” said Harry, starting to feel
angry.  
“**Yeah, okay,” said Ron, in exactly the same sceptical tone as
Cedric**. “Only you said this morning you’d have done it last night,
and no one would’ve seen you. . . . I’m not stupid, you know.”  
“You’re doing a really good impression of it,” Harry snapped.  
“Yeah?” said Ron, and there was no trace of a grin, forced or otherwise,
on his face now.  
<sub>—*Goblet of Fire*, Chapter 17, The Four Champions</sub>  

In *Order of the Phoenix*, the wizarding community seems intent in rejecting that Voldemort has returned, so that includes accusing Harry (and Dumbledore) of lying.

I can understand why people who aren't close to Harry disbelieve him when he claims that Voldemort killed Cedric, especially when the Ministry wants to spread the false narrative that Cedric died in a tragic accident, but why do some of his friends, like Seamus, honestly believe that Harry would orchestrate such a lie about Cedric's death and Voldemort? It's not as if Harry had a reputation to warrant the strong suspicion (on the contrary).

I can understand why fear and the propaganda is convincing people that Harry is lying, and in the case of Seamus, his mum's opinion is also a factor, but to have been friends (and in the case of Seamus shared a bedroom) for 5 years with Harry, who doesn't have a reputation of lying (in fact the opposite), and to still suspect strongly that he is orchestrating this dark lie about Cedric's death and Voldemort's return (for what, attention?) doesn't make sense to me.

> “That’s out of order, Seamus,” said Ron, whose ears were starting to
glow red, always a danger sign.  
“Out of order, am I?” shouted Seamus, who in contrast with Ron was turning paler. “**You believe all the rubbish he’s come out with**  about You-Know-Who, do you, you reckon he’s telling the truth?”  
“Yeah, I do!” said Ron angrily.  
“Then you’re mad too,” said Seamus in disgust.  
<sub>—*Order of the Phoenix*, Chapter 11, The Sorting Hat's New Song</sub>