Learn Italian: A sentire il proprietario, il prezzo non è trattabile. - To hear the owner tell it, the price is not negotiable.

The structure a + infinitive forms an implicit conditional clause. It essentially means 'if one hears.' While you could use secondo il proprietario (according to the owner) for a similar meaning, a sentire adds a slight nuance of skepticism. It highlights that this is merely what the owner claims, perfectly matching the English 'to hear the owner tell it.'

If I wanted to make this conditional clause explicit instead of using a + infinitive, how would I phrase it?

You would use a standard se (if) clause. For example, you could say se sentiamo il proprietario (if we hear the owner) or use the impersonal form se si sente il proprietario (if one hears the owner). The implicit a sentire is just a more concise and idiomatic option.

Usually, the subject of an infinitive has to match the subject of the main clause. Why doesn't it match here?

You are right that implicit clauses generally require the same subject as the main clause. However, phrases like a sentire..., a giudicare da... (to judge by), or a guardare... (to look at) act as fixed idiomatic exceptions. The unstated subject of the infinitive is a general 'we' or 'one' (if one hears the owner), which doesn't need to match the main subject (il prezzo).

How does the word trattabile break down, and is it common in everyday Italian?