kanrihi ga omotta yori takakatta node, keiyakusyo no naiyou wo mou itido syuuseisite moraimasita.

Because 管理費 is the subject of 高かった in the reason clause.

• 管理費が高かった = the management fee was high
• Here, the sentence is explaining a fact: the fee turned out to be higher than expected.

You could sometimes see は in similar sentences, but が is very natural here because it presents the fee as the thing that had the property high.

So:

• 管理費が高かったので = because the management fee was high
• 管理費は高かったので would sound more like the fee is already the topic and now you are commenting on it.

より means than, and in Japanese the comparison standard does not always need a noun after it.

• 思ったより高かった = was higher than I thought
• Literally: than I thought, it was high

This pattern is very common:

• 想像したより難しい = harder than I imagined
• 見た目より軽い = lighter than it looks

So 思ったより works like a set phrase meaning:

• than expected
• than I had thought

You do not need to add something like もの or こと here.

Because the thought or expectation happened before the speaker learned the actual amount.

• 思う = to think
• 思った = thought

So 思ったより means:

• than I thought
• than I had expected

In English, this often feels like than expected, but Japanese naturally uses the past form because the expectation existed earlier.

Japanese often uses the past tense when talking about how something turned out in a particular situation.

Here, the speaker is looking back on the management fee and saying it turned out to be high relative to what they had expected.

So:

• 高いので = because it is high
• 高かったので = because it was high / turned out to be high

In this sentence, 高かった sounds natural because it refers to the amount as it was found or understood during the contract process.

Both can mean because, but the nuance is different.

• ので sounds softer, more explanatory, and a bit more formal
• から sounds more direct and sometimes more personal or assertive

So:

• 高かったので、修正してもらいました sounds calm and explanatory
• 高かったから、修正してもらいました is also correct, but a little more direct

In written or polite explanatory situations, ので is very common.

Because the thing being revised is the content of the contract, not necessarily the physical document itself.

• 契約書 = contract document
• 契約書の内容 = the contents of the contract

So:

• 契約書を修正する can mean revise the contract
• 契約書の内容を修正する is more explicit: revise what is written in it

This phrasing makes it clear that the terms/details were changed.

もう一度 means once more or again.

Here it modifies 修正してもらいました:

• もう一度修正してもらいました = had it revised one more time / had them revise it again

It shows that a revision had already happened before, or that the speaker is asking for a repeat revision.

You can think of it as an adverb placed before the verb phrase.

This is the pattern:

• て-form + もらう

It means to receive the favor/benefit of someone doing something for you.

So:

• 修正してもらいました does not mean I revised it
• It means I had someone revise it for me or someone revised it for me

The focus is on the speaker as the receiver of the action.

Breakdown:

• 修正して = revise and...
• もらいました = received the favor

Very natural English translations include:

• I had them revise it again
• I got the contents of the contract revised again

The sentence does not say explicitly.

That is very normal in Japanese. The person is omitted because the context probably makes it clear. It could be:

• the real estate agent
• the landlord
• the company
• the person handling the contract

The important point is that it was not presented as the speaker doing it personally. If the speaker revised it themselves, the sentence would more naturally be:

• 契約書の内容をもう一度修正しました

But with 修正してもらいました, someone else did the revision and the speaker benefited from it.

This is standard Japanese sentence structure.

In polite Japanese, subordinate clauses usually stay in plain form, and the main verb at the end carries the politeness.

So this is normal:

• 思った
• 高かった
• ので
• もらいました

Even though 思った and 高かった are plain forms, the sentence as a whole is polite because it ends with もらいました.

This happens all the time:

• 時間がなかったので、行きませんでした
• 雨が降っていたので、帰りました

Yes, but the focus would change.

• 修正してもらいました = I had someone revise it for me / I received that favor
• 修正してくれました = they revised it for me

Both involve someone doing something beneficial for the speaker, but:

• もらう focuses on the receiver
• くれる focuses on the giver

So:

• 契約書の内容をもう一度修正してもらいました highlights that the speaker got the revision done
• 契約書の内容をもう一度修正してくれました highlights that someone kindly did it

The original sentence is very natural if the speaker wants to describe the situation from their own side.

Because Japanese often leaves out information that is understood from context.

In this sentence, several things are omitted:

• who thought it would be cheaper
• whose contract it was
• who revised it

A native speaker can often infer these from the situation. Most likely:

• the speaker thought the fee would be lower
• the speaker had someone revise the contract

This is one of the biggest differences from English. Japanese does not need to state every subject if it is already clear enough.