Ввиду того, что объявленная ценность высокая, таможенную пошлину проверят.

Ввиду того, что is a formal way to say because, since, or in view of the fact that.

It is grammatically correct, but it sounds more official or bureaucratic than everyday speech. In conversation, Russians would more often say:

• потому что — because
• так как — since / because
• поскольку — since / given that

So this sentence has a somewhat formal, administrative tone.

Yes, this is a very common question.

In this sentence, ввиду is written as one word because it functions like a preposition/conjunction meaning because of or in view of.

• ввиду того, что ... = because ...
• ввиду плохой погоды ... = because of bad weather ...

The spelling в виду as two words exists too, but it usually has a more literal meaning related to having something in sight / keeping something in mind, for example:

• иметь в виду = to mean / to keep in mind

So here, ввиду must be one word.

Because the sentence is a complex sentence with a subordinate clause first and the main clause second.

Structure:

• Ввиду того, что объявленная ценность высокая = subordinate clause
• таможенную пошлину проверят = main clause

In Russian, when the subordinate clause comes first, it is separated from the main clause by a comma.

So the comma after высокая marks the end of the subordinate clause.

Объявленная is a passive participle formed from the verb объявить.

Here it means something like declared.

It behaves like an adjective and agrees with ценность in gender, number, and case:

• ценность — feminine singular nominative
• объявленная — feminine singular nominative

So объявленная ценность literally means declared value.

In practice, you can often think of participles like this as adjective-like words built from verbs.

Both are possible, but they have slightly different style and tone.

• высокая = full adjective form
• высока = short adjective form

In this sentence, объявленная ценность высокая is perfectly normal and neutral.

A version with the short form would be:

• объявленная ценность высока

That sounds a bit more formal or bookish. Russian often allows both full and short predicate adjectives, but the full form is very common in everyday language.

Because it is the direct object of the verb проверят.

The verb проверить / проверять takes a direct object: you check something.

So:

• пошлина = nominative
• пошлину = accusative

And the adjective must agree with it:

• таможенная пошлина = nominative
• таможенную пошлину = accusative

That is why both words change form.

Проверят is the 3rd person plural future of the perfective verb проверить.

So it means they will check.

Because the verb is perfective, the future is a simple future:

• проверить → проверят

This often has an indefinite-personal meaning in Russian: the sentence does not name who exactly will do it, but it implies some people or officials will.

So here, проверят means something like:

• they will check
• it will be checked
  depending on how natural the English translation is in context

Russian very often uses the 3rd person plural without an explicit subject to mean people / officials / someone.

So проверят does not necessarily mean a specific group already mentioned. It can just mean that the relevant people will do it.

In this customs context, the implied subject is something like:

• customs officers
• postal staff
• officials

This is a very normal Russian pattern.

In this kind of context, ценность is understandable and can be appropriate, especially in postal or customs language, where объявленная ценность is a set expression meaning declared value.

In more general everyday language, learners often know стоимость better for cost / price / value.

Very roughly:

• стоимость = cost, price, monetary value
• ценность = value, worth, importance

But in administrative language, объявленная ценность is a standard phrase, especially for parcels and insured shipments.

So in this sentence, ценность is not strange.

Yes. The sentence begins with the reason, then gives the result:

• Ввиду того, что объявленная ценность высокая, ...
• ..., таможенную пошлину проверят.

This is a normal and logical order in Russian, especially in formal writing.

You could also put the main clause first, but this version foregrounds the reason. That fits the official tone.

It is grammatical and understandable, but a native speaker might slightly adjust it depending on the exact meaning.

Two things stand out:

1. Ввиду того, что is quite formal.
2. проверят таможенную пошлину can sound a little unusual if the intended meaning is they will check the amount/calculation of the customs duty.

A more natural version might be:

• Ввиду того, что объявленная ценность высокая, проверят размер таможенной пошлины.
• Поскольку объявленная ценность высокая, таможенную пошлину пересчитают.

That said, the original sentence is still understandable, and for a learner it is a useful example of formal written Russian.