Họ đoán gói cước này tốt.

Họ means they.

It is a third-person plural pronoun, so it refers to more than one person. In this sentence, họ is the subject: the people doing the guessing.

A quick pattern:

• họ = they
• đoán = guess
• gói cước này tốt = this plan is good

So the structure is basically They guess (that) this plan is good.

In Vietnamese, demonstratives like này (this) usually come after the noun, not before it.

So:

• gói cước này = this plan
• literally: plan this

This is normal Vietnamese word order.

Compare:

• cuốn sách này = this book
• người này = this person
• ý tưởng này = this idea

So gói cước này is exactly the expected pattern.

Gói cước is a noun phrase meaning something like plan, service plan, pricing package, or tariff package, depending on context.

It is commonly used for things like:

• phone plans
• mobile data plans
• internet plans
• subscription pricing packages

So in many real situations, gói cước này could mean:

• this mobile plan
• this data package
• this subscription plan

The exact English translation depends on the situation.

No. In gói cước, gói is part of the noun itself, not a classifier.

It forms a compound noun with cước:

• gói = package/bundle
• cước = fee/rate/charge

Together, gói cước means a pricing package or plan.

So this is different from a true classifier structure such as:

• một gói bánh = one package of cookies

In your sentence, gói cước is best understood as one combined noun.

Because Vietnamese often does not use a copula like English is before adjectives.

So:

• gói cước này tốt = this plan is good
• literally closer to: this plan good

This is a very important Vietnamese pattern. Adjectives can act like predicates by themselves.

Examples:

• Cô ấy đẹp. = She is beautiful.
• Trời nóng. = The weather is hot.
• Món này ngon. = This dish is delicious.

So tốt works directly as the predicate here.

Usually, no—not in normal neutral Vietnamese.

With adjectives like tốt, Vietnamese normally does not use là.

Natural:

• Gói cước này tốt.

Unnatural or at least much less standard in this basic sense:

• Gói cước này là tốt.

A useful rule for learners:

• before adjectives: usually no là
• before nouns in identity statements: là is common

For example:

• Anh ấy là bác sĩ. = He is a doctor.
• Gói cước này tốt. = This plan is good.

Yes. It can be a complete sentence on its own:

• Gói cước này tốt. = This plan is good.

In your example, that whole clause is functioning as the content of đoán:

• Họ đoán [gói cước này tốt].
• They guess [that this plan is good].

So the sentence contains a main clause plus an embedded clause.

Vietnamese often leaves out a word equivalent to English that when introducing a content clause.

So:

• Họ đoán gói cước này tốt.
• literally: They guess this plan good.
• natural English: They guess that this plan is good.

The linker is simply omitted.

In some contexts, Vietnamese can use words like rằng or sometimes là after verbs of saying/thinking, but they are not necessary here.

So you may also encounter:

• Họ đoán rằng gói cước này tốt.

That sounds more explicit or slightly more formal.

Not exactly.

Đoán usually means:

• guess
• make a guess
• infer
• sometimes predict, depending on context

It suggests less certainty than nghĩ (think).

So:

• Họ đoán gói cước này tốt. = They guess this plan is good.
• Họ nghĩ gói cước này tốt. = They think this plan is good.

If the English meaning shown to the learner is They think this plan is good, then the Vietnamese sentence still works only if the idea is closer to they’re guessing / they assume rather than a firm opinion.

No tense is explicitly marked here.

Vietnamese often does not mark tense unless it needs to. The sentence can be understood from context.

So Họ đoán gói cước này tốt could mean:

• They guess this plan is good.
• They guessed this plan was good.
• They are guessing this plan is good.

If you want to make time clearer, Vietnamese can add time words or aspect markers, for example:

• Hôm qua họ đoán gói cước này tốt. = Yesterday they guessed this plan was good.
• Họ đang đoán gói cước này tốt. = They are guessing this plan is good.

Because tốt is the predicate adjective of the clause gói cước này tốt.

Vietnamese often follows this pattern:

• subject/topic + adjective

So:

• gói cước này = this plan
• tốt = good

Together:

• gói cước này tốt = this plan is good

Putting tốt at the end is completely normal here.

Gói cước tốt này means something like this good plan.

That is a noun phrase, not a full statement.

Compare:

• gói cước này tốt = this plan is good

  • full clause
  • tốt is the predicate

• gói cước tốt này = this good plan

  • noun phrase
  • tốt describes gói cước inside the noun phrase

So word order changes the structure and meaning.

Yes, it is grammatically natural.

However, whether đoán is the best verb depends on the exact intended meaning.

If the idea is truly guess, then this sentence is fine:

• Họ đoán gói cước này tốt.

If the idea is more like they think / they believe / they consider, Vietnamese speakers might more often say:

• Họ nghĩ gói cước này tốt.
• Họ cho rằng gói cước này tốt.

So the grammar is good; the main nuance question is the choice of đoán.