Learn Hardcore Turkish: Peşin ödeme yaparsan küçük bir indirim oluyor. - If you pay in cash upfront, there’s a small discount.

Peşin means upfront/in advance (not on credit or in installments). It says nothing about the payment method. You can pay peşin by cash, card, or bank transfer—what matters is that you pay all at once before receiving the goods/services.
Nakit specifically means cash (banknotes/coins). So:

peşin ödeme = advance/full upfront payment (any method)
nakit ödeme = cash payment (the method is cash)

Why use ödeme yapmak instead of just ödemek? Can I say Peşin ödersen?

Yes, you can say Peşin ödersen; it’s perfectly natural and a bit shorter.
Ödeme yapmak is a very common “light-verb” expression meaning “to make a payment.” Both are fine:

Peşin ödeme yaparsan... = If you make an advance payment...
Peşin ödersen... = If you pay in advance...

How is yaparsan formed? Why not yaparsın?

Yaparsan is conditional: yap-ar-sa-n = do-AOR-COND-2SG → “if you do.”
Yaparsın is plain aorist 2SG: “you (usually) do.”
So:

yaparsan = if/when you do
yaparsın = you do (as a habit), or “you would do” in some contexts

Why is it oluyor and not olur or var?

All three can work but they feel different:

oluyor (progressive) sounds like “there tends to be / there’s usually,” a soft, conversational way to state a typical outcome, often implying current practice: “these days, if you pay in advance, there’s a small discount.”
olur (aorist) states a general rule: “there will be / there is (as a rule).”
var is a bare “there is”: küçük bir indirim var = there is a small discount (existence), without the dynamic “it happens” feel.

Could I say küçük bir indirim yapılıyor instead?

Yes. Küçük bir indirim yapılıyor is passive: “a small discount is given.”
Nuance:

indirim oluyor = “a discount happens/there is a discount” (impersonal, very common)
indirim yapılıyor = “a discount is being given” (passive, also common)
With an explicit subject: küçük bir indirim yapıyorlar = “they give a small discount”

Is bir necessary in küçük bir indirim?

It’s strongly preferred. Bir plays the role of “a/an.” With adjectives, Turkish almost always uses bir for an indefinite singular noun:

Natural: küçük bir indirim
Less natural/more categorical: küçük indirim (sounds like you’re talking about “small discount” as a general category)

Can I swap the clauses? Where do commas go?

Yes:

Standard: Peşin ödeme yaparsan, küçük bir indirim oluyor.
Also fine: Küçük bir indirim oluyor, peşin ödeme yaparsan.
When the conditional clause comes second, a comma before it is normal.

How do I make it polite or formal?

Use the plural/polite second person or a nominal construction:

Peşin ödeme yaparsanız, küçük bir indirim oluyor/olur.
More formal: Peşin ödemeniz hâlinde/durumunda küçük bir indirim olur.

What’s the negative version?

Peşin ödeme yapmazsan, indirim olmuyor/olmaz. = If you don’t pay in advance, there isn’t a discount.
Using olmaz states a rule; olmuyor sounds like “there tends not to be.”

Does -sa/-se mean “if” or “when” here?

It can mean either, depending on context. With the aorist stem (yapar-sa-n), it often has a generic “if/whenever” sense. Here it’s basically “if you pay in advance,” but “when(ever) you pay in advance” also fits.

How do I say the size of the discount (e.g., 10%)?

Use yüzde + number:

Peşin ödersen yüzde on indirim olur/oluyor/var. = If you pay in advance, there’s a 10% discount.

Any pronunciation tips for ö, ş, and stress in this sentence?

ö: rounded front vowel, like French eu in peur; somewhat like British “sir” without the r.
ş: “sh” in “shoe.”
Stress is usually on the last stressed syllable of the word. In practice here:
- peşín
- ödém(e) (final stress: ödeMÉ)
- yapárs(a)n (main stress on -par-; the -san ending is light)
- küçük often feels like final stress (küçúk) in isolation
- indirim → indiRÍM
Oluyor is oluYÓR (the progressive is -(I)yor; after o, the high vowel is u → oluyor).

Where is “you” in the sentence? Do I need to add sen?

“you” is built into yaparsan (the -n is 2nd person singular). You don’t need sen. You can add sen for emphasis or contrast: Sen peşin ödeme yaparsan...