It might show the constant power struggle between them. Harry, as a wizard, has an inner strength that the Dursleys try to suppress with their mundane and cruel ways. So it's a battle of wills.
Well, the Dursleys were extremely cruel to Harry. They locked him in his cupboard under the stairs for a long time. They also tried to prevent him from knowing about his magical heritage, which was a big part of who he was. Harry must have felt a great deal of resentment towards them for suppressing his true self.
One popular 'Harry Hates the Dursleys' fanfiction could be 'The Dursley's Worst Nightmare'. In this fic, Harry finally stands up to the Dursleys in a very assertive way. He uses his magic not to harm them but to make them understand how much they've wronged him.
Well, in the original story, the Dursleys are really mean to Harry. So, fans want to explore more about Harry's feelings towards them. It gives an opportunity to write about his pent - up anger and frustration.
In the 'the dursleys abuse harry fanfiction', the abuse can be multi - faceted. Physically, Harry could be pushed around or hit by Vernon. Emotionally, Petunia might constantly compare him unfavorably to Dudley, which is really damaging to Harry's self - esteem. And socially, they might prevent him from having any friends over, making him feel completely alone in the world.
It's possible. In some fanfictions, authors might explore complex motives for the Dursleys' actions. Maybe they could be under some dark magic influence that makes them act out of character and in a more extreme way. However, this goes against the general perception of the Dursleys in the original series, where they are mainly just cruel and neglectful without such extreme murderous intent.
One consequence could be that Harry becomes withdrawn. He's so used to the abuse that he doesn't trust people easily. He might have nightmares often, reliving the moments of abuse. For instance, if Vernon has hit him before, he could have flashbacks in his sleep.
Well, in fanfic, the Dursleys' abuse of Harry can be shown in different ways. They might isolate him from the outside world. For instance, not allowing him to have friends or participate in normal neighborhood activities. They could also starve him, giving him very little food while Dudley gets plenty. This kind of treatment is often explored in detail in fanfiction to show how harsh Harry's life is with the Dursleys.
One way the Dursleys can be good in fanfiction is if they are forced to face the consequences of their actions early on. For instance, they might receive a warning from the wizarding world that if they don't treat Harry well, there will be serious repercussions. So they start to be nicer to him. They could provide him with a proper room, better food, and allow him to have friends over.
In some Harry Potter fanfictions, the Dursleys are depicted as nice. This could be a really interesting take. It might show how they could have been different if they hadn't been so influenced by their dislike for magic. Maybe they could have supported Harry more, or at least been less cruel. For example, a fanfiction could explore a scenario where Vernon Dursleys actually encourages Harry's academic achievements at school, instead of always putting him down.