"Zijn er in het winkelcentrum meubels te koop?"

Furniture is a mass noun in English and uses a singular conjugation ("is").

However, the Dutch translation ("meubels") is plural, so it uses the conjugation "zijn".

In Australia a shopping mall is quite small compared to a shopping centre. Shopping malls are usually single-level, while shopping centres are often multi-level. Most shopping centres have one or more supermarkets, while shopping malls are mostly composed of small shops. You're more likely to find franchises or chain stores in a shopping centre than in a mall which tend to be more beautique.

When I went to to Amsterdam, I visited a shopping centre. It was a very small building (by Australian standards) with only about 40 chain stores over four storeys. So the Dutch concept of a shopping centre mightn't match very closely with the Australian or American idea.

for sale = te koop (noun)

to buy = kopen (verb)