Breakdown of На чьём аукционе эксперт оценивал эту редкую вещь?
этот
this [f: эта, n: это]
чей
whose (m, sister forms: чья, чьё)
на
on, at / by (transport) / to (a place) / to (in answer to)
вещь
thing
Questions & Answers about На чьём аукционе эксперт оценивал эту редкую вещь?
Why is "whose" translated as чьём in this sentence?
It modifies аукционе (auction), which is in the prepositional case because of the preposition на (at). Since аукцион is a masculine noun, the pronoun чей (whose) must take the masculine prepositional form, which is чьём.
Why do we use the preposition на instead of в for "at the auction"?
In Russian, events, activities, and public gatherings (like an auction, a concert, or a meeting) almost always take the preposition на rather than в to indicate location.
Why doesn't the word вещь change its ending in эту редкую вещь?
This phrase is the direct object of the sentence, so it is in the accusative case. вещь is a feminine noun that ends in a soft sign (3rd declension). For these nouns, the accusative form is identical to the nominative. You can tell it's accusative here because its modifiers, эту and редкую, take the standard feminine accusative endings.
Why is the imperfective verb оценивал used here instead of the perfective оценил?