После покупки я оставила отзыв, потому что сервис оказался лучше ожиданий.

Because после normally requires the genitive case.

• покупка = nominative singular
• покупки = genitive singular

So:

• после покупки = after the purchase / after buying

This is a very common pattern:

• после урока = after the lesson
• после работы = after work
• после встречи = after the meeting

Покупка is a noun meaning purchase or buying.

In после покупки, it means something like:

• after the purchase
• after buying it

Russian often uses a noun where English might prefer a clause. So instead of saying after I bought it, Russian can naturally say after the purchase.

Оставила is the past tense, perfective, feminine singular form of оставить.

It tells us:

• the action happened in the past
• it was completed
• the speaker is female

So:

• я оставил = I left / posted / submitted ... (male speaker)
• я оставила = I left / posted / submitted ... (female speaker)

This is one of the first places English speakers notice that Russian past tense agrees with gender.

Because the two verbs agree with different subjects.

• я оставила → the subject is я, and the speaker is female, so the verb is feminine
• сервис оказался → the subject is сервис, which is a masculine noun, so the verb is masculine

So the gender of the past-tense verb depends on the noun or pronoun doing that action.

This is an aspect question.

• оставить = perfective
• оставлять = imperfective

Here оставила отзыв means the speaker completed the action of leaving/posting the review. That is why perfective fits well.

Compare:

• Я оставила отзыв. = I left/posted a review.
  Completed fact.
• Я оставляла отзывы там раньше. = I used to leave reviews there before / I was leaving reviews there.
  More about process, repetition, or background.

In this sentence, the speaker is talking about one completed action, so оставила is the natural choice.

Отзыв here means review or feedback.

In many everyday contexts, especially online, оставить отзыв is the standard phrase for:

• leaving a review
• posting feedback
• writing a review

Examples:

• оставить отзыв о товаре = leave a review about a product
• оставить отзыв о магазине = leave a review about the store

So я оставила отзыв is a very common collocation.

Оказался comes from оказаться, which often means:

• turned out to be
• proved to be

So сервис оказался лучше ожиданий means:

• the service turned out to be better than expected

This is different from plain был:

• сервис был лучше ожиданий = the service was better than expectations
• сервис оказался лучше ожиданий = the service turned out to be better than expectations

Оказался adds the idea of a result that became clear after experience. It often suggests surprise or a contrast with what was expected.

Because лучше is the comparative form of хороший:

• хороший = good
• лучше = better
• лучший = best

Here the sentence is comparing the service with expectations:

• сервис оказался лучше ожиданий = the service turned out better than expectations

You would use лучший when you mean best or the best:

• это лучший сервис = this is the best service

So:

• лучше = better
• лучший = best

After a comparative like лучше, Russian often uses the genitive to express than.

So:

• лучше ожиданий = better than expectations

Here:

• ожидания = expectations
• ожиданий = genitive plural

This is a very common pattern:

• выше среднего = higher than average
• меньше нормы = less than the norm
• лучше плана = better than the plan

Russian can also use чем for comparisons, but with words like лучше the genitive construction is very natural and compact.

Because Russian often leaves out possessive words when they are obvious from context.

In English, you might naturally say:

• better than my expectations

In Russian, if it is clear that these are the speaker’s expectations, just ожиданий is enough.

Both are possible:

• лучше ожиданий = better than expectations
• лучше моих ожиданий = better than my expectations

Adding моих makes it more explicit, but the shorter version sounds very natural.

Yes, absolutely.

Compare:

• сервис оказался лучше ожиданий = the service turned out better than expectations
• сервис оказался лучше, чем я ожидала = the service turned out better than I expected

The second version is more personal and explicit. The original sentence is a bit more compact and formal-sounding.

Both are natural.

Потому что means because and introduces the reason.

So the sentence structure is:

• Я оставила отзыв = I left a review
• потому что сервис оказался лучше ожиданий = because the service turned out better than expectations

This is one of the most common ways to say because in Russian.

Other options exist, such as так как, but потому что is very common in everyday speech and writing.

The word order is fairly flexible, though some versions sound more natural than others.

Original:

• После покупки я оставила отзыв, потому что сервис оказался лучше ожиданий.

Possible variations:

• Я оставила отзыв после покупки, потому что сервис оказался лучше ожиданий.
• Потому что сервис оказался лучше ожиданий, я оставила отзыв после покупки.

The original sounds natural and neutral. Starting with После покупки nicely sets the time frame first.

Russian word order often changes for emphasis, flow, or style more than for basic grammar.

It depends on context. Сервис is a broad word in Russian and can mean:

• service quality
• customer service
• a service/platform/app
• sometimes even a company’s overall service experience

In this sentence, сервис оказался лучше ожиданий most likely means something like:

• the service was better than expected
• the overall service experience turned out better than expected

If the context were about a website or app, сервис could also mean the platform itself.

Yes, it is natural and idiomatic.

Why it sounds natural:

• после + genitive is correct
• оставить отзыв is a standard collocation
• потому что is a very common way to give a reason
• оказался лучше ожиданий is a natural way to say turned out better than expected

It sounds like something a native speaker could write in a review or say when explaining why they posted one.