Aĉetanto kontrolas la broĉon kaj antikvaĵon.

In Esperanto, -as marks the present tense. So kontrolas means checks / is checking.

A few useful comparisons:

• kontrolas = checks
• kontrolis = checked
• kontrolos = will check
• kontrolu = check! (command)
• kontroli = to check

So in this sentence, kontrolas tells you the action is happening in the present.

The -n ending marks the direct object in Esperanto.

Here, the buyer is doing the checking, and the things being checked are:

• la broĉon
• antikvaĵon

So both nouns take -n because they are the objects of kontrolas.

This is one of the most important Esperanto endings:

• aĉetanto = the subject, the one doing the action
• broĉon = object
• antikvaĵon = object

Because the two objects are joined by kaj, each one is still understood as an object, so each gets -n.

Because aĉetanto is the subject, not the object.

In Esperanto, the subject usually has no special ending, while the direct object takes -n.

So:

• Aĉetanto = the buyer, the one performing the action
• kontrolas = checks
• la broĉon kaj antikvaĵon = the things being checked

That is why only the objects have -n here.

Aĉetanto is built from several parts:

• aĉet- = buy
• -ant- = someone doing the action
• -o = noun ending

So aĉetanto literally means a person who is buying or more naturally buyer.

This pattern is very common in Esperanto:

• lernanto = learner, student
• parolanto = speaker
• vendanto = seller

So once you recognize -ant-, words like this become much easier to understand.

Esperanto does not use the definite article as often as English does, and it has no indefinite article like a or an.

So aĉetanto can mean something like:

• a buyer
• the buyer, depending on context

If you specifically wanted to say the buyer, you could say:

• La aĉetanto kontrolas la broĉon kaj antikvaĵon.

Without la, it sounds more like a buyer or buyer in a general/context-based sense.

In Esperanto, one la can apply to both nouns when they are joined by kaj.

So:

• la broĉon kaj antikvaĵon

can be understood as:

• the brooch and the antique

You could also repeat the article:

• la broĉon kaj la antikvaĵon

That is also correct. Repeating la may sound a little more explicit, but it is not required.

Antikvaĵon comes from:

• antikv- = ancient / old
• -aĵ- = a thing characterized by something
• -o = noun
• -n = direct object

So antikvaĵo means an antique object, antique, or curio.

The suffix -aĵ- is useful because it often turns a quality or idea into a concrete thing:

• bela = beautiful

• belaĵo = a beautiful thing

• nova = new
• novaĵo = news / a new thing

So antikvaĵo is literally something characterized by being old or ancient.

The most noticeable special letters here are:

• ĉ = like ch in church
• ĵ = like zh, the sound in measure or vision

So approximately:

• Aĉetanto ≈ a-che-TAHN-to
• broĉon ≈ BRO-chon
• antikvaĵon ≈ an-tee-KVA-zhon

A few pronunciation reminders:

• Esperanto stress is usually on the second-to-last syllable
• each letter has a consistent sound

So:

• a-ĉe-TAN-to
• BRO-ĉon
• an-ti-KVA-ĵon

They are singular.

In Esperanto:

• -o = singular noun
• -oj = plural noun
• -on = singular direct object
• -ojn = plural direct object

So:

• broĉon = one brooch
• antikvaĵon = one antique

If there were more than one of each, you would have:

• broĉojn
• antikvaĵojn

Yes, Esperanto word order is fairly flexible because the -n ending helps show what is the object.

The most neutral order is the one in your sentence:

• Aĉetanto kontrolas la broĉon kaj antikvaĵon.

But other orders are possible, for example:

• La broĉon kaj antikvaĵon kontrolas aĉetanto.

That said, the standard subject–verb–object order is usually the clearest and most natural for learners.

Yes.

You can say:

• Aĉetanto kontrolas la broĉon kaj antikvaĵon.
• Aĉetanto kontrolas la broĉon kaj la antikvaĵon.

Both are grammatical.

Using la only once is normal when one article clearly applies to both nouns. Repeating it can make the structure a little more explicit, but it is not necessary.