Das Gerät ist mangelhaft, und der Verkäufer erstattet Geld.

Because in German, all nouns are capitalized.

So in this sentence:

• das Gerät = the device
• der Verkäufer = the seller
• Geld = money

But verbs and adjectives are not capitalized here:

• ist = is
• mangelhaft = defective / faulty
• erstattet = refunds / reimburses

This is one of the most noticeable differences from English spelling.

Because Gerät is a neuter noun in German.

German nouns have grammatical gender, so you have to learn the noun together with its article:

• der = masculine
• die = feminine
• das = neuter

So you learn:

• das Gerät

In this sentence, das is the nominative singular article because das Gerät is the subject of the first clause.

Because mangelhaft comes after the verb ist and is being used as a predicate adjective.

After verbs like sein (to be), German adjectives usually do not take endings:

• Das Gerät ist mangelhaft.

But if the adjective comes before a noun, then it does take an ending:

• ein mangelhaftes Gerät
• das mangelhafte Gerät

So:

• ist mangelhaft = no adjective ending
• mangelhaftes Gerät = adjective ending required

Here, mangelhaft means something like defective, faulty, or not up to standard.

It is a useful word in product, warranty, and legal/customer-service contexts. It can sound a bit more formal or technical than a simple word like schlecht (bad).

So for a product, mangelhaft suggests that it has a defect or a problem, not just that it is generally bad.

This is a normal main clause in German, and German main clauses follow the verb-second rule.

That means the finite verb must be in the second position:

• Das Gerät = first element
• ist = second element
• mangelhaft = rest of the clause

So the pattern is:

• Subject + finite verb + complement

This is very common in simple statements.

Because und joins two main clauses, and the second clause keeps normal main-clause word order.

So this is fine:

• Das Gerät ist mangelhaft und der Verkäufer erstattet Geld.

In the second clause:

• der Verkäufer = subject
• erstattet = finite verb in second position
• Geld = object

German does not automatically move the verb just because the clause comes after und.

You would only see a different order if some other element came first, for example:

• ..., und dann erstattet der Verkäufer das Geld.

Here dann takes the first position, so the verb erstattet stays second, before the subject.

Erstattet is the 3rd person singular present tense form of erstatten.

So the verb is:

• erstatten = to refund / reimburse

And here:

• der Verkäufer erstattet = the seller refunds / reimburses

A few useful forms:

• ich erstatte = I refund
• du erstattest = you refund
• er/sie/es erstattet = he/she/it refunds
• wir erstatten = we refund

It is a weak verb, so its past forms are regular:

• erstattete = refunded
• hat erstattet = has refunded

Because Verkäufer is a masculine noun, so its dictionary form is:

• der Verkäufer

In this sentence, it is the subject of the second clause, so it is in the nominative case, and the article stays der.

If it were a direct object instead, you might see:

• den Verkäufer

So here:

• der Verkäufer = nominative subject

Also, Verkäufer means seller or salesman, depending on context.

German sometimes uses a noun like Geld without an article, especially when speaking in a more general or abstract way.

So Geld here works as the direct object of erstattet.

However, in this particular context, many learners should know that das Geld may sound more natural if you mean a specific amount of money already known from context:

• Der Verkäufer erstattet das Geld.

That sounds more like the seller refunds the money.

Without the article, Geld can sound a bit more general, almost like refunds money as a general action.

It is the accusative case, because it is the direct object of the verb erstattet.

The action is being done by:

• der Verkäufer = the subject

And the thing being refunded is:

• Geld = the direct object

Because Geld appears here without an article, you cannot see the case from the article itself. But its function in the sentence is still accusative.

Usually, no.

In standard German, you normally do not use a comma before und when it simply connects two main clauses:

• Das Gerät ist mangelhaft und der Verkäufer erstattet Geld.

So the version without the comma is usually the standard choice.

A comma before und can appear in special cases for clarity or because of extra structure in the sentence, but in a simple sentence like this, it is normally omitted.

It is understandable, but a native speaker might often choose a slightly more natural version, especially with the object.

For example:

• Das Gerät ist mangelhaft und der Verkäufer erstattet das Geld.
• Das Gerät ist mangelhaft und der Verkäufer erstattet den Kaufpreis.

The second version is especially natural in formal or commercial contexts, because den Kaufpreis means the purchase price.

If you want to mention who receives the refund, you could also say:

• Der Verkäufer erstattet dem Käufer den Kaufpreis.

So the original sentence is grammatical enough for learning, but in real usage German often prefers a more specific object than just Geld.