Der Verkäufer erstattet den Kaufpreis.

Because in German, all nouns are capitalized. That is a standard spelling rule.

So here:

• Verkäufer = a noun
• Kaufpreis = a noun

Articles like der and den, and verbs like erstattet, are not capitalized unless they begin a sentence.

It is singular here.

You can tell because:

• the article is der, not die
• the verb is erstattet, which is 3rd person singular

Compare:

• Der Verkäufer erstattet den Kaufpreis. = singular
• Die Verkäufer erstatten den Kaufpreis. = plural

A useful thing to remember is that Verkäufer has the same form in singular and plural, so the article and verb help you identify which one it is.

This is about case.

• der Verkäufer is the subject of the sentence, so it is in the nominative
• den Kaufpreis is the direct object, so it is in the accusative

Both nouns are masculine singular, so the article changes like this:

• nominative: der
• accusative: den

That is why you get:

• der Verkäufer
• den Kaufpreis

Here, erstattet means refunds or reimburses.

The verb is erstatten. In money-related contexts, it is often used for:

• refunding a purchase price
• reimbursing costs
• repaying expenses

It sounds a bit more formal or business-like than some everyday alternatives.

For example:

• Der Verkäufer erstattet den Kaufpreis.
• Die Firma erstattet die Reisekosten.

One thing to know: erstatten can also mean something else in a different context, for example:

• Anzeige erstatten = to file a report / make a police report

So the exact meaning depends on the object and the situation.

In this sentence, erstattet is 3rd person singular present tense:

• ich erstatte
• du erstattest
• er / sie / es erstattet
• wir erstatten
• ihr erstattet
• sie / Sie erstatten

It is not a separable verb. The er- prefix stays attached.

So you say:

• Der Verkäufer erstattet den Kaufpreis.

And in the perfect tense:

• Der Verkäufer hat den Kaufpreis erstattet.

Not geerstattet.

Kaufpreis is a compound noun:

• Kauf = purchase
• Preis = price

So Kaufpreis means purchase price.

It is a little more precise and often more formal than just saying Preis. You will often see it in:

• contracts
• returns and refunds
• legal or business language

So den Kaufpreis erstatten is a very natural phrase in formal German for refund the purchase price.

German can leave that out if it is already clear from context.

So:

• Der Verkäufer erstattet den Kaufpreis.

simply focuses on what is being refunded.

If you want to include the person receiving the money, you usually add a dative object:

• Der Verkäufer erstattet dem Kunden den Kaufpreis.

Here:

• dem Kunden = to the customer
• den Kaufpreis = the purchase price

So German can have both:

• recipient in the dative
• thing refunded in the accusative

Because German main clauses normally follow the verb-second rule.

In this sentence:

• Der Verkäufer = first element
• erstattet = second element

So:

• Der Verkäufer erstattet den Kaufpreis.

If you move another element to the front, the verb still stays second:

• Den Kaufpreis erstattet der Verkäufer.

That version is grammatical too, but it puts more emphasis on den Kaufpreis.

Literally, yes: der Verkäufer is the masculine form and usually refers to a male seller.

The feminine form is:

• die Verkäuferin

Plural:

• die Verkäufer
• die Verkäuferinnen for an all-female group

In some contexts, masculine forms are also used in a generic way, especially in traditional or less explicitly inclusive language. But if you specifically mean a woman, you would normally say die Verkäuferin.

Because the sentence is treating both nouns as specific or contextually known:

• der Verkäufer = the seller
• den Kaufpreis = the purchase price

This often happens when the situation is already understood, for example in a return or refund context.

You could use indefinite articles in another context, but the meaning would change:

• Ein Verkäufer erstattet einen Kaufpreis.

That sounds more abstract or less natural in this situation, because normally we mean the seller involved in the transaction and the specific price that was paid.

A rough English-friendly guide:

• der ≈ dair or short dehr
• Verkäufer ≈ fer-KOI-fer
• erstattet ≈ air-SHTAT-et
• den ≈ dane
• Kaufpreis ≈ KOWF-price

A few important pronunciation points:

• German v in Verkäufer is pronounced like f
• äu is pronounced like English oi
• au is pronounced like English ow in cow
• ei is pronounced like English eye

So the trickiest word for many learners is Verkäufer:

• ver- is unstressed
• stress falls on -käu-

So it sounds roughly like fer-KOI-fer.