Mal feilscht eine Kundin, mal handelt sie den Verkaufspreis herunter.

Here mal ... mal ... is a fixed pattern meaning something like:

• sometimes ... sometimes ...
• at one time ... at another ...
• now ... now ...

So Mal feilscht eine Kundin, mal handelt sie den Verkaufspreis herunter means that one thing happens in one instance, and another thing happens in another instance.

Important: this is not the same as the everyday modal particle mal in sentences like Komm mal her.

Because mal takes the first position in the clause, and in German the finite verb normally comes in second position in a main clause.

So the structure is:

• Mal = position 1
• feilscht = position 2
• eine Kundin = the rest

That is why you get:

• Mal feilscht eine Kundin ...
• not Mal eine Kundin feilscht ...

The second clause works the same way:

• mal = position 1
• handelt = position 2
• sie = after the verb

Feilschen means to haggle or to bargain over a price, usually in a back-and-forth way.

It often suggests trying to get a better deal by arguing over the price. It can sound a little vivid or expressive, and sometimes slightly negative depending on context.

Example idea:

• Auf dem Markt feilscht er um jeden Euro. = He haggles over every euro at the market.

So in your sentence, feilscht describes the customer negotiating the price.

They are related, but not identical.

• feilschen focuses on the act of haggling
• handeln ... herunter focuses on the result of bargaining something down

So:

• feilschen = to haggle
• den Verkaufspreis herunterhandeln = to negotiate the sale price down

In other words, the first clause describes the bargaining activity, while the second clause describes successfully reducing the price.

Eine Kundin means a female customer.

German often marks gender in nouns for people:

• der Kunde = male customer / customer in the masculine form
• die Kundin = female customer

The article eine is used because Kundin is feminine.

If the customer were masculine, it would be:

• Mal feilscht ein Kunde ...

Sie refers back to eine Kundin.

Since Kundin is feminine singular, the correct pronoun is:

• sie = she

So the sentence avoids repeating eine Kundin:

• Mal feilscht eine Kundin, mal handelt sie den Verkaufspreis herunter.

This is very natural German.

Den Verkaufspreis herunterhandeln means to negotiate the sale price down.

Breakdown:

• der Verkaufspreis = the sale price
• herunterhandeln = to bargain down / negotiate down

So the whole phrase means that the customer gets the price reduced through negotiation.

This is a separable verb:

• infinitive: herunterhandeln
• in a main clause: sie handelt den Verkaufspreis herunter

That is why herunter appears at the end.

Because herunterhandeln takes a direct object in the accusative case.

The thing being negotiated down is the sale price, so it becomes the accusative object:

• nominative: der Verkaufspreis
• accusative: den Verkaufspreis

So:

• sie handelt den Verkaufspreis herunter

If you used der Verkaufspreis, that would be grammatically wrong here.

Both, depending on the form.

The infinitive is written as one word:

• herunterhandeln

But in a normal main clause, the prefix separates:

• Sie handelt den Verkaufspreis herunter.

This is because it is a separable verb.

You will also see forms like:

• Sie hat den Verkaufspreis heruntergehandelt.
• Den Verkaufspreis herunterzuhandeln ist schwierig.

On its own, handeln can have several meanings, including:

• to trade
• to deal
• in some contexts, to be about as in Es handelt sich um ...

But here the combination herunterhandeln makes the meaning clear: it means to negotiate down.

So learners should focus on the full verb:

• herunterhandeln
• not just handeln

There is a comma because the sentence contains two main clauses:

• Mal feilscht eine Kundin
• mal handelt sie den Verkaufspreis herunter

Each part could stand on its own as a clause, so the comma separates them.

This is very normal in German when two coordinated clauses are placed side by side.

Yes, it is natural and idiomatic.

It has a slightly descriptive, written feel because of the repeated mal ... mal ... pattern. It sounds like someone is describing what happens in different cases or from time to time.

The verbs are also quite specific:

• feilschen is more expressive than a plain verb like verhandeln
• den Verkaufspreis herunterhandeln is precise and idiomatic

So the sentence is good German, especially in explanatory or narrative contexts.

Yes. That would also be correct.

The difference is mostly stylistic:

• mal ... mal ... sounds more compact and rhythmical
• manchmal ... manchmal ... is more explicit and straightforward

So both work, but the original version is a bit more elegant or literary in tone.

Very often, yes. A common pattern is:

• um + accusative

For example:

• Sie feilscht um den Preis.
• Er feilscht um jeden Cent.

In your sentence, the object of bargaining is not stated directly with feilschen, because the sentence then switches to the more specific phrase den Verkaufspreis herunterhandeln in the second clause.

So learners should know:

• feilschen often appears with um
• but here it is used without stating the price explicitly