This is the 15795th most frequent Russian word.
продавший
"Продавший" means "one who has sold" or "having sold."
Here, 'продавший' functions as a past participle describing 'человек', indicating that the person has performed the selling action.
Человек, продавший свою машину, теперь ищет новый автомобиль.
The person who sold their car is now looking for a new vehicle.
In this sentence, 'продавшаяся' is a reflexive past participle describing 'книга', showing that the book itself was sold successfully.
Книга, продавшаяся за рекордную сумму, стала знаменитой.
The book that sold for a record amount became famous.
Here, 'продавшая' serves as a past participle referring to 'компания', denoting the entity that performed the selling.