La rabato havas efikon sur la aĉetanton.

Because efikon is the direct object of havas.

• La rabato = the subject, the thing that has
• havas = has
• efikon = the thing being had, so it takes the accusative -n

In Esperanto, the -n ending often marks the direct object. So:

• rabato = subject
• efikon = direct object

That is why you get La rabato havas efikon.

This is a very common learner question.

Normally, after a preposition, you do not need -n, because the preposition already shows the relationship. But with certain prepositions of place or direction, including sur, Esperanto can add -n to show direction toward a target.

Here that idea is being used figuratively:

• sur la aĉetanto = on the buyer
• sur la aĉetanton = onto / directed toward the buyer

So the sentence presents the effect as something aimed at or landing on the buyer.

In abstract expressions like this, you may also encounter sur la aĉetanto without -n. The version with -n adds a stronger sense of directed impact.

Aĉetanto comes from:

• aĉet- = buy
• -ant- = active present participle, someone doing the action
• -o = noun

So aĉetanto literally means someone who buys / a buyer / purchaser.

That is different from aĉetisto:

• -ist- usually means a professional, specialist, or habitual person connected with something

So:

• aĉetanto = buyer, purchaser
• aĉetisto = more like a professional buyer, purchasing agent, or someone whose role is buying

In this sentence, aĉetanto is the natural choice.

Esperanto often allows both a noun phrase and a simple verb.

Here:

• havas efikon sur ... = has an effect on ...
• a shorter alternative would be influas ... or efikas sur ...

So these are all possible kinds of wording:

• La rabato havas efikon sur la aĉetanton.
• La rabato influas la aĉetanton.
• La rabato efikas sur la aĉetanton.

The version with havas efikon is perfectly understandable and feels a bit more formal or analytical.

Because both nouns are being treated as specific or identifiable in the context.

• la rabato = the specific discount being discussed
• la aĉetanton = the specific buyer being referred to

In Esperanto, la works much like the in English. If the speaker has a particular discount and a particular buyer in mind, la is natural.

Yes, sur is a natural choice with words like efiko and influo when talking about something affecting a target.

It matches the idea of something having an impact on someone or something.

So expressions like these are normal:

• efiko sur iu
• influo sur iu

A learner may expect some other preposition because Esperanto does not always match English exactly, but in this case sur is a very reasonable and common-looking choice.

Yes. Esperanto word order is fairly flexible because endings show grammatical roles.

The neutral order here is:

• La rabato = subject
• havas = verb
• efikon = direct object
• sur la aĉetanton = prepositional phrase

So this is a standard subject–verb–object sentence.

Because efikon has -n, Esperanto can move things around more easily than English can. For example, a speaker could change the order for emphasis. But for learners, the original order is the clearest and most natural starting point.

A few pronunciation points are useful here:

• ĉ is pronounced like ch in church
• Esperanto stress is almost always on the second-to-last syllable

So the stress goes like this:

• ra-BA-to
• HA-vas
• e-FI-kon
• sur
• la
• a-ĉe-TAN-ton

That makes aĉetanton sound roughly like ah-cheh-TAHN-ton.

Once you know ĉ and the regular stress rule, the whole sentence becomes much easier to say correctly.