Prodavac je potvrdio zamenu.

This is the normal past tense in Serbian, called the perfect.

It is formed with:

• the auxiliary je = has / did-type past marker
• the past participle potvrdio = confirmed

So:

• je = 3rd person singular of jesam (to be)
• potvrdio = masculine singular past participle of potvrditi (to confirm)

Together, je potvrdio means confirmed / has confirmed.

In everyday English, you usually just translate it as confirmed.

Because the past participle must agree with the subject in gender and number.

The subject here is prodavac, which is:

• masculine
• singular

So the verb form is:

• potvrdio = masculine singular

Compare:

• Prodavac je potvrdio zamenu. = a male salesperson confirmed the exchange/replacement
• Prodavačica je potvrdila zamenu. = a female salesperson confirmed it
• Prodavci su potvrdili zamenu. = the salespeople confirmed it

Because it is the direct object of the verb, so it goes into the accusative case.

The base form is:

• zamena = nominative singular

But after a transitive verb like potvrditi, you need the accusative:

• zamenu = accusative singular

This is a very common pattern for feminine nouns ending in -a:

• poruka → poruku
• narudžbina → narudžbinu
• zamena → zamenu

So potvrditi zamenu means to confirm the exchange/replacement.

It is in the nominative singular, because it is the subject of the sentence.

Base form:

• prodavac = seller / salesperson

Here it answers the question who confirmed?

• Prodavac je potvrdio zamenu.

So:

• prodavac = nominative singular
• zamenu = accusative singular

That subject-object contrast is one of the key things Serbian cases show.

It can mean either one, depending on context.

Serbian does not have articles like the and a/an. So prodavac by itself can be:

• the salesperson
• a salesperson
• sometimes even the seller

You figure it out from context.

So Prodavac je potvrdio zamenu. could be understood as:

• The salesperson confirmed the exchange or
• A salesperson confirmed the exchange

Because je is a clitic, and clitics in Serbian usually go in second position in the sentence or clause.

Here the first unit is Prodavac, so the clitic je comes right after it:

• Prodavac je potvrdio zamenu.

This is very natural Serbian word order.

You will see the same pattern in many sentences:

• Marija je došla.
• Kupac je pitao.
• Radnik je završio posao.

So the placement of je is not random; it follows a common Serbian rule.

Yes, Serbian word order is fairly flexible, but the focus or style changes.

The most neutral version is:

• Prodavac je potvrdio zamenu.

Other orders are possible, for example:

• Zamenu je potvrdio prodavac. = it was the salesperson who confirmed the exchange
• Potvrdio je zamenu prodavac. = more marked, often used for emphasis or in narration

So the meaning stays basically the same, but the sentence may sound more:

• emphatic
• contrastive
• literary
• context-dependent

For learners, the given order is the safest default.

Potvrditi is perfective.

That means it presents the action as completed, as a whole event:

• the confirmation happened and was completed

That fits this sentence well, because the exchange/replacement has already been confirmed.

The imperfective partner is usually:

• potvrđivati

Very roughly:

• potvrditi = to confirm, once / successfully / completely
• potvrđivati = to be confirming / to confirm repeatedly / habitually / over a period of time

So:

• Prodavac je potvrdio zamenu. = the confirmation was completed

In standard full sentences, normally no.

The correct standard form is:

• Prodavac je potvrdio zamenu.

If you remove je:

• Prodavac potvrdio zamenu

that sounds incomplete in normal standard Serbian, though you might see something like that in:

• headlines
• notes
• very informal speech
• certain regional or colloquial styles

For learners, it is best to keep the full past-tense form with je.

Yes. Prodavac is the standard Serbian word for salesman / seller / salesperson.

If you are comparing Serbian with Croatian, you may also notice:

• prodavač is more typical in Croatian
• prodavac is standard in Serbian

In Serbian, the feminine form is:

• prodavačica = female salesperson

So in this sentence, prodavac is completely normal Serbian.

In Serbian, many masculine nouns do not end in -o. In fact, a lot of masculine nouns end in a consonant, and prodavac is one of them.

So:

• prodavac = masculine noun
• it triggers masculine agreement: je potvrdio

This is very common:

• kupac je došao
• radnik je rekao
• prodavac je potvrdio

A consonant ending is often a clue that a noun is masculine, though of course there are exceptions you learn over time.