In a 'Harry sold rescued Snape' fanfiction, the plot could start with Harry learning that Snape is held captive by a group of dark wizards. Harry realizes that he needs certain magical supplies or potions to break Snape free. Since he doesn't have the funds to buy these items, he decides to sell a rare spell book that he found in the Room of Requirement. This spell book has some unique spells that could potentially be used against the dark wizards. But once he sells it, he discovers that the buyer has some ulterior motives and is somehow connected to the group holding Snape. Now Harry has to not only get the spell book back but also figure out how to use it to rescue Snape while dealing with the new threats that have emerged.
There might be a 'Harry sold rescued Snape' fanfiction, but it's not a very common or well - known concept from what I've seen. You could try searching on specialized Harry Potter fanfiction communities. Maybe some of the more niche ones might have a story like this. However, it also depends on how unique the idea is within the vast world of fanfiction. If it's too out - there, it might be a rare find.
One possible plotline could be Harry being sold due to some dark magic plot against him. Snape then has to deal with this unexpected situation and protect Harry from further harm. Another could be that it's a part of a deal to save the wizarding world, and Snape and Harry must learn to work together in this strange new dynamic.
In this fanfiction, it could be that Stryker has been seeking a powerful being like Harry for a long time. When Harry is sold to him, Stryker first tries to study Harry's magic. Harry initially feels hopeless but then discovers a weakness in Stryker's security or plans. He uses his intelligence and the magic he still has access to, despite being in a difficult situation, to turn the tables on Stryker and eventually escape. This could also lead to Harry bringing down Stryker's whole operation to prevent others from being sold or used in the future.
One possible plot could be that Harry is wrongly accused of a crime in the wizarding world, perhaps something related to dark magic. The police, who might be a new magical law enforcement unit, rescue him from an angry mob. They then help him clear his name by finding the real culprit, who could be a Death Eater in disguise trying to frame Harry to cause chaos in the post - Voldemort era.
The plot could involve the goblins rescuing Harry when he is being wrongly accused of a crime in the wizarding world. They could believe in his innocence and use their unique skills and knowledge of magic to keep him safe. Maybe they help him prove his innocence later on. They might also have their own motives for helping Harry, like they see him as a key to some sort of change in the relationship between wizards and goblins.
The plot might start with a magical experiment gone wrong. Harry ends up with a special mark or power that makes him Snape's master. As the story progresses, Harry uses this power to make Snape teach him advanced potions and dark arts defenses. Snape resents it but has no choice. Meanwhile, Voldemort senses this strange new power dynamic and tries to use it to his advantage. This forces Harry and Snape to work together in ways they never thought possible to outwit Voldemort while also dealing with their own difficult relationship.
Maybe in the fanfiction, Voldemort devises a plan where Snape forgets Harry to disrupt the Order of the Phoenix's plans. Without Snape's knowledge of Harry and his role in the prophecy, things start to go awry. Harry has to find a way to make Snape remember, perhaps by going on a quest to find a magical relic that can restore memories. Hermione and Ron would be by his side, of course, providing their usual support and knowledge.
In this kind of fanfiction, perhaps Harry is rescued by the Order of the Phoenix earlier than in the original story. They might have realized the Dursleys' mistreatment sooner. Then Harry could start his magical training earlier, away from the hostile environment of the Dursleys' home. He may also form closer bonds with other members of the Order, like Sirius, who could play a more active role in his upbringing.
One possibility could be that Voldemort rescues Harry Potter for some self - serving reason. Maybe he realizes that Harry holds the key to a greater power that he wants to obtain. So, instead of killing Harry, he saves him from another threat, like a powerful dark wizard who is trying to overthrow Voldemort and sees Harry as a useful tool as well. In this fanfiction, Harry would be in a very strange situation, having to trust Voldemort at least temporarily.
There are likely some out there. Fanfiction writers often come up with creative and unexpected scenarios. You could start by using the search terms 'Harry sold to Snape' on different fanfiction websites. Some might be well - written with interesting character developments based on this strange premise.