Les frais de retour sont compris dans le remboursement.

In French, frais is very often used as a plural noun meaning fees, costs, charges, or expenses.

So les frais de retour literally looks like the return costs/fees.

A native English speaker may expect a singular idea, like the return fee, but French commonly uses the plural here. That is normal in expressions like:

• les frais de port = shipping costs
• les frais de dossier = admin fees
• les frais de livraison = delivery charges

Also, frais has the same spelling in singular and plural, so the article les and the verb sont are what clearly show that it is plural here.

It looks the same, but here it is a noun, not an adjective.

• un produit frais = a fresh product
• les frais = fees/costs/expenses

So in this sentence, frais has nothing to do with freshness. It is a completely different use of the same form.

De retour means for return or related to returning something.

In les frais de retour, the structure is:

• frais = fees/costs
• de retour = of return / for return

So the whole phrase means return fees/costs, often specifically return shipping costs depending on context.

This noun + de + noun pattern is extremely common in French:

• une carte de crédit = a credit card
• un billet de train = a train ticket
• des frais de retour = return fees

Because the subject is les frais de retour, which is plural.

So the verb must also be plural:

• les frais ... sont
• not les frais ... est

And compris agrees with frais:

• compris = masculine plural
• comprise = feminine singular
• comprises = feminine plural

Since frais is masculine plural, compris is the correct form.

No. Here compris means included, not understood.

That can be confusing, because compris is the past participle of comprendre, which often means to understand.

But in expressions like être compris dans, it means:

• to be included in
• to be part of

So:

• Je comprends = I understand
• C’est compris dans le prix = It is included in the price

This is a very common business/customer-service use of compris.

Dans here means in in the sense of as part of.

So compris dans le remboursement means:

• included in the refund
• part of the refund amount

French often uses dans after compris or inclus:

• compris dans le prix = included in the price
• inclus dans l’offre = included in the offer
• compris dans le remboursement = included in the refund

So dans is the natural preposition here.

Because de retour is describing the type or purpose of the fees.

In French, when one noun defines another, French often uses:

• noun + de + noun

without an article after de.

That is why you get:

• frais de retour
• frais de livraison
• ticket de bus
• salle de bain

Adding an article there would usually sound wrong or would change the meaning.

Remboursement is a noun meaning refund or reimbursement.

It comes from the verb rembourser, which means to reimburse or to refund.

Compare:

• rembourser = to refund / to reimburse
• un remboursement = a refund / a reimbursement

So in this sentence, le remboursement is the refund.

Yes. That would be perfectly natural.

Both compris dans and inclus dans can mean included in.

So these are both fine:

• Les frais de retour sont compris dans le remboursement.
• Les frais de retour sont inclus dans le remboursement.

In many contexts, inclus may sound a little more immediately transparent to learners, but compris is very common in formal or customer-service French.

French is focusing first on what is being included.

So the structure is:

• Les frais de retour = the thing being talked about
• sont compris = are included
• dans le remboursement = in the refund

English could also do this:

• Return fees are included in the refund

If French wanted to focus on the refund instead, it could use a different structure, for example:

• Le remboursement comprend les frais de retour.

That means roughly The refund includes the return fees.

A simple pronunciation guide is:

Les frais de retour sont compris dans le remboursement
lay fray duh ruh-toor son kom-pree don luh ron-boors-mon

A few useful points:

• les frais sounds like lay fray
• retour has a French r
• sont has a nasal vowel, roughly son without a strong English n
• remboursement also has nasal sounds at the end

You do not pronounce every final consonant strongly the way you might in English.