The Passive Voice

Sentences of the type Fruit is sold at the market are called passive voice sentences. Passive voice sentences are a way to express the result of an action without having to identify the agent of the action:

• Mrs. Sanchez sells fruit in the market. (active voice)
  Fruit is sold in the market. (passive voice)

In English, the passive voice is preferred when the agent of the action is unknown or unimportant:

• Fruit is sold in the market.

However, in Spanish, when the the agent of the action is unknown or unimportant, the preference is usually (but not always) for either the active voice:

• Venden fruta en el mercado. -- They sell fruit in the market.

or the reflexive:

• Se vende fruta en el mercado. -- (literally) Fruit sells itself in the market.

In Spanish, when the agent of the action is known or implied, a true passive voice sentence using ser + past participle may be used:

• La fruta es vendida en el mercado por la Señora Sanchez. -- Fruit is sold in the market by Mrs. Sanchez.

Since the participle functions as an adjective, it must reflect the gender and number of the noun being described:

• Las manzanas son vendidas por la Señora Sanchez. -- The apples are sold by Mrs. Sanchez. 

However, it is more likely that a Spanish speaker would use the active voice:

• La Señora Sánchez vende fruta en el mercado. -- Mrs. Sanchez sells fruit in the market.
  La Señora Sánchez vende manzanas. -- Mrs. Sanchez sells apples.

Another possibility, if the agent is not known or not important:

• Se venden manzanas. -- (literally) Apples sell themselves in the market. --> Apples are for sale in the market.