Die verkoper stal porselein en erdewerk uit.

Because the full verb is uitstal, meaning to display or to lay out for display. In Afrikaans, many verbs are separable verbs. In a normal main clause, the first part stays with the finite verb and the second part moves to the end:

• uitstal → stal ... uit

So:

• Die verkoper stal porselein en erdewerk uit.

But in places where the verb is not split, you get:

• Ek weet dat die verkoper porselein en erdewerk uitstal.
• Die verkoper wil porselein en erdewerk uitstal.

This is very common in Afrikaans.

No. That is a very common confusion for English speakers.

Here, stal ... uit comes from uitstal, which means display.

The verb to steal in Afrikaans is steel:

• Hy steel geld. = He steals money.

So:

• stal ... uit = displays
• steel = steals

Even though stal may look like an English past tense such as stole, that is not what is happening here.

Verkoper means seller, salesperson, or vendor, depending on context.

It comes from the verb verkoop, meaning to sell:

• verkoop = sell
• verkoper = seller

So die verkoper is simply the seller / the salesperson.

Depending on the situation, it could refer to someone in a shop, at a market, or any person selling goods.

Yes. In Afrikaans, die is the definite article for both singular and plural nouns:

• die verkoper = the seller
• die verkopers = the sellers

Unlike languages such as German or Dutch, Afrikaans does not have different definite articles for grammatical gender. So you do not have to learn separate forms like the for masculine, feminine, or neuter nouns. It is simply die.

Because here they are being used as general materials or categories of goods, not as single countable objects.

So:

• porselein = porcelain
• erdewerk = earthenware / pottery

This works much like English:

• The seller displays porcelain and earthenware.

In English, you would not normally say the seller displays a porcelain and an earthenware. Afrikaans works similarly here.

If you wanted to talk about individual items, you would use countable nouns instead, for example:

• porseleinstukke = porcelain pieces
• erdewerkstukke = earthenware pieces

They refer to two different kinds of ceramic goods.

• porselein = porcelain, usually finer, harder, and often more delicate-looking
• erdewerk = earthenware, pottery made from clay and fired at lower temperatures

So the sentence suggests the seller is displaying different types of ceramic items.

In many contexts, erdewerk can sound a bit broader or more traditional than just pottery.

Usually no. Afrikaans verbs are much simpler than English verbs in this respect. The verb generally stays the same regardless of the subject.

So you get:

• Ek stal uit.
• Jy stal uit.
• Hy stal uit.
• Ons stal uit.
• Hulle stal uit.

This is one of the easier parts of Afrikaans grammar for English speakers.

Yes. This is standard Afrikaans main-clause word order.

The structure is:

• Die verkoper = subject
• stal = finite verb
• porselein en erdewerk = object
• uit = separated verb particle

So the pattern is basically:

Subject + finite verb + object + particle

That is normal for a separable verb in a main clause.

In a subordinate clause, the separable verb is usually written together again as uitstal, and the verb goes to the end.

For example:

• Ek weet dat die verkoper porselein en erdewerk uitstal.

So compare:

• Main clause: Die verkoper stal porselein en erdewerk uit.
• Subordinate clause: ... dat die verkoper porselein en erdewerk uitstal.

This is a very useful pattern to learn early.

Yes, possibly. Uitstal often means display, but it can also carry the idea of setting out, laying out, or arranging for display, depending on context.

So the focus is not only that the items are visible, but often that they are being presented to customers in an intentional way.

That is why display is usually the best English translation, but set out for display may sometimes be closer.