Learn Italian: Il mercato all'ingrosso vende la stoffa al metro. - The wholesale market sells the fabric by the meter.

Italian uses the preposition a to express rates, distribution, and prices. When talking about units of measurement like metro or chilo, this a must combine with the definite article to form an articulated preposition, which is why we get al metro instead of just a metro or a literal translation like per il metro.

Is the phrase all'ingrosso also an example of the rate-marking preposition?

No, it is a fixed phrase that means "wholesale" or "in bulk". It uses the articulated preposition all' (combining a and l') before the noun ingrosso, but it acts as a descriptive adverbial phrase rather than a rate. For contrast, the phrase for selling "retail" is al dettaglio.

If I wanted to say the market sells fabric "by weight", would I still use the articulated preposition al?

Yes! Following the exact same rule for rates and units of measurement, you would use the preposition a combined with the definite article for the word peso (weight), resulting in the phrase al peso.

Could I drop the article in la stoffa and just say vende stoffa?