Learn Polish: Przed wyprzedażą trzeba było odrestaurować te antyki. - Before the sale, it was necessary to restore these antiques.

Trzeba (it is necessary / one must) is an impersonal word, meaning it doesn't take a subject like a normal verb. To make it past tense, you just add the third-person singular neuter form of the verb to be, which is było. Together, trzeba było means "it was necessary" or "one had to."

Why is the word for "sale" spelled wyprzedażą here?

The preposition przed (before) requires the Instrumental case. The base form is wyprzedaż, which is a feminine noun that ends in a consonant. To form the Instrumental for this type of noun, you simply add -ą to the end, resulting in wyprzedażą.

Could I use the imperfective verb restaurować instead of the perfective odrestaurować?

Using the perfective odrestaurować emphasizes that the antiques needed to be completely restored before the sale. If you used the imperfective restaurować, it would sound like it was only necessary to spend some time working on them, without necessarily finishing the job.

What case is te antyki in this sentence?

It is in the Accusative case because it is the direct object of the verb odrestaurować. For masculine inanimate objects like antyk, the Accusative plural form is identical to the Nominative plural. This is why both the demonstrative pronoun (te) and the noun (antyki) look exactly like their basic plural forms.