Dia bukannya tawar-menawar, melainkan memborong semuanya.

It sets up a contrast: not X, but rather Y or instead of X, Y.

So:

• bukannya tawar-menawar = not bargaining / instead of bargaining
• melainkan memborong semuanya = but rather buying everything up

This pattern often suggests that the second action is the surprising or real one.

In this kind of sentence, bukannya is the more natural form before a verb-like or clause-like idea.

A useful rule of thumb is:

• bukan often negates nouns or noun phrases
  
  • Dia bukan dokter. = He/She is not a doctor.
• bukannya often introduces a contrast involving an action or expectation
  
  • Bukannya pergi, dia malah tidur. = Instead of leaving, he/she actually slept.

Here, tawar-menawar refers to an action, so bukannya fits well.

The -nya here is not possessive. It is part of the fixed expression bukannya ... melainkan ....

Melainkan means but rather and is used when the first part has been negated or rejected.

So the logic is:

• not X, melainkan Y
• not X, but rather Y

That makes it stronger and more corrective than tetapi/tapi, which usually just means but.

Compare:

• Dia bukan guru, melainkan dosen.
  = He/She is not a schoolteacher, but rather a lecturer.
• Dia lelah, tetapi tetap bekerja.
  = He/She was tired, but kept working.

In your sentence, melainkan is perfect because the first idea is being rejected: he/she did not bargain; instead, he/she bought everything.

Also, melainkan sounds a bit more formal or polished than tapi.

Tawar-menawar means bargaining, haggling, or negotiating a price.

It is a reduplicated form, and the repetition suggests a back-and-forth process, which matches the idea of bargaining.

Related forms:

• menawar = to make an offer / bargain / bid
• tawar-menawar = bargaining, haggling, negotiation

In everyday use, tawar-menawar often refers specifically to price negotiation in a market or shop.

The hyphen is standard in writing for this reduplicated form.

It is often treated as a noun-like expression meaning bargaining or negotiation, but in sentences like this it functions very naturally as the action being contrasted.

So even though English may translate it as a verb:

• He/She wasn’t bargaining...

Indonesian is comfortable using a form like tawar-menawar in this kind of slot without needing to mark it exactly the way English would.

You can think of it as:

• bukannya tawar-menawar = not doing any bargaining

So the sentence is completely natural.

Memborong means to buy up in bulk, to buy a whole lot at once, or to buy everything available.

It comes from borong, which is connected with buying wholesale or taking the whole lot.

So this is stronger than just membeli (to buy). It suggests that the person did not just buy something—they bought a large quantity, possibly all the items being sold.

In this sentence, memborong semuanya gives the idea of:

• buying all of it
• snapping everything up
• taking the whole lot

Semua means all.

Semuanya means all of it or all of them, with a more complete, definite feel.

So:

• semua = all
• semuanya = all of it / all of them / everything

In this sentence, memborong semuanya sounds very natural because it refers to the whole set of relevant things—everything on sale, everything in the display, everything available, depending on context.

Because the same subject applies to both parts of the contrast.

The structure is:

• Dia = he/she
• bukannya tawar-menawar = instead of bargaining
• melainkan memborong semuanya = but rather bought everything

Indonesian often avoids repeating the subject when it is already clear.

So this is understood as:

• He/She was not bargaining; rather, he/she bought everything.

Repeating dia would usually be unnecessary here.

Either one.

Dia is gender-neutral, so by itself it can mean:

• he
• she

You only know the gender from context, not from the pronoun itself.

That is very common in Indonesian.

Yes, very much.

Bukannya ... melainkan ... often carries the feeling of contrary to what you might expect.

So the sentence does not just state two facts. It suggests something like:

• You might expect this person to haggle over the price...
• but instead, they bought everything.

That makes the sentence feel a bit emphatic or dramatic.

Yes. A more conversational version could be:

• Dia bukannya nawar, malah memborong semuanya.

Here:

• nawar is a casual form related to menawar
• malah means instead, actually, or on the contrary, often with a surprising tone

This sounds more everyday and spoken.

The original sentence with melainkan is perfectly correct, but slightly more formal or literary.