Learn Dutch: De piano's in deze winkel zijn erg duur. - The pianos in this store are very expensive.

In Dutch, nouns that end in a single open vowel (like a, i, o, u, or y) get an 's to make them plural. If you just wrote pianos, Dutch spelling rules would make the o sound short. The apostrophe protects the long vowel sound from the singular word.

Why is it deze winkel and not dit winkel?

The word for store is a de word (de winkel). When you want to say 'this' with a de word, you always use deze. You only use dit with het words.

Why doesn't duur get an -e at the end (dure) since the pianos are plural?

When an adjective comes after a verb like zijn (to be), it doesn't get an extra -e ending. You only add the -e when the adjective is placed directly before the noun, such as in de dure piano's (the expensive pianos).

Could I use heel instead of erg in this sentence?

Yes, you can! Heel duur and erg duur both mean 'very expensive' and are completely interchangeable here.