Apesar do defeito, a vendedora aceitou trocar o produto na mesma hora.

Apesar de means despite or in spite of.

So:

• apesar do defeito = despite the defect

The form do is a contraction:

• de + o = do

So apesar de o defeito becomes apesar do defeito.

This kind of contraction is very common in Portuguese:

• de + a = da
• de + os = dos
• de + as = das

For example:

• apesar da demora = despite the delay
• apesar dos problemas = despite the problems

It can be used with both.

In your sentence, it is followed by a noun phrase:

• apesar do defeito = despite the defect

But it can also be followed by a verb, usually in the infinitive or in a clause. For example:

• Apesar de estar com defeito, o produto foi trocado.
  = Despite being defective, the product was exchanged.

• Apesar de chover, eles saíram.
  = Despite it raining, they went out.

So apesar de is a very flexible structure.

Because Apesar do defeito is an introductory phrase placed before the main clause.

The sentence is structured like this:

• Apesar do defeito, = introductory concessive phrase
• a vendedora aceitou trocar o produto na mesma hora. = main clause

In English, we also often use a comma after an opening phrase like Despite the defect, ...

In Portuguese, this comma is very natural and helps readability.

Portuguese often uses definite articles more than English does.

So where English might say:

• the saleswoman
• or sometimes just saleswoman in certain contexts

Portuguese very naturally says:

• a vendedora

This is normal with many nouns, including professions and people already understood in the context.

For example:

• O médico chegou. = The doctor arrived.
• A professora explicou tudo. = The teacher explained everything.

Leaving out the article is sometimes possible, but in this sentence a vendedora is the most natural form.

Vendedora means saleswoman or female salesperson.

It is the feminine form of:

• vendedor = salesman / male salesperson
• vendedora = saleswoman / female salesperson

The ending -a here marks feminine gender.

So if the employee were male, the sentence would be:

• Apesar do defeito, o vendedor aceitou trocar o produto na mesma hora.

Aceitou is the preterite form of aceitar.

• aceitar = to accept / to agree
• aceitou = accepted / agreed

It is third person singular, matching a vendedora:

• a vendedora aceitou = the saleswoman accepted / agreed

The preterite is used because this is a completed action in the past.

Compare:

• aceitou = she agreed / accepted
• aceitava = she used to agree / was agreeing / would agree, depending on context

In this sentence, aceitou shows a single completed past action.

This is a very common structure in Portuguese:

• aceitar + infinitive

It means to agree to do something or to accept doing something.

So:

• aceitou trocar = agreed to exchange

Other examples:

• Ela aceitou esperar. = She agreed to wait.
• Ele aceitou ajudar. = He agreed to help.

The first verb is conjugated:

• aceitou

The second verb stays in the infinitive:

• trocar

Here trocar means to exchange or to replace.

In a store context, trocar o produto usually means:

• to exchange the product for another one
• or to replace it

It does not mean to change in the general sense of changing yourself or changing an idea.

Some useful comparisons:

• trocar o produto = exchange/replace the product
• trocar de roupa = change clothes
• mudar de ideia = change one’s mind

So in this sentence, the store employee agreed to replace or exchange the defective item.

Again, Portuguese commonly uses the definite article where English may or may not.

• o produto = the product

In a sentence about a specific item already being discussed, the article sounds natural and expected.

Portuguese usually prefers:

• trocar o produto rather than
• trocar produto

Without the article, it would sound less natural in this context.

Na mesma hora literally means at the same hour, but in real usage it usually means:

• right away
• immediately
• on the spot

So in this sentence, it means the saleswoman agreed to exchange the product immediately.

It is made of:

• em + a = na
• mesma = same
• hora = hour / time

So:

• na mesma hora = at that very moment / right then

Similar expressions:

• imediatamente = immediately
• na hora = right away / at the time
• na mesma hora = right away, that very moment

Because mesma agrees with hora, and hora is feminine.

• o mesmo dia = the same day
• a mesma hora = the same hour / the same time

In Portuguese, words like mesmo/mesma often agree in gender and number with the noun they describe:

• mesmo problema
• mesma loja
• mesmos produtos
• mesmas condições

So here:

• hora is feminine singular
• therefore mesma is feminine singular too

It is understandable, but in natural English, accepted to exchange sounds less idiomatic. A better translation would usually be:

• the saleswoman agreed to exchange the product
• the saleswoman agreed to replace the product
• the saleswoman accepted the exchange right away depending on context

In Portuguese, aceitar + infinitive is normal. In English, agree to + verb is often the most natural equivalent.

So:

• aceitou trocar = agreed to exchange

is usually the best choice.

Yes, some changes are possible.

The original sentence is very natural:

• Apesar do defeito, a vendedora aceitou trocar o produto na mesma hora.

You could also say:

• A vendedora aceitou trocar o produto na mesma hora, apesar do defeito.

This still makes sense, though the original order is a bit more elegant and common because it sets up the contrast first.

You could also replace na mesma hora with another time expression:

• Apesar do defeito, a vendedora aceitou trocar o produto imediatamente.

So the word order has some flexibility, but the original sentence is perfectly natural Brazilian Portuguese.

Yes, defeito is a very natural word here.

Defeito means:

• defect
• fault
• flaw

In the context of a product, it usually means something is wrong with it in a manufacturing or functional sense.

For example:

• O celular veio com defeito. = The phone came defective.
• O aparelho tem um defeito. = The device has a defect.

It is more specific than problema:

• problema = problem
• defeito = defect / fault

So defeito is especially appropriate for store, warranty, and product-return situations.