Questions & Answers about Lo sconto è valido solo se comprate all'ingrosso.
How does the preposition a function in the phrase all'ingrosso?
It acts as a rate or manner preposition. Combined with the definite article l', the preposition a describes the scale at which the buying happens. This is the same distributive use of a you see in phrases like al chilo (per kilo) or al metro (per meter).
What is the literal meaning of ingrosso?
If all'ingrosso means "wholesale," how do you say "retail" using this same structure?
You say al dettaglio (literally, "by the detail" or "piece by piece"). Just like all'ingrosso, it uses the rate-marking preposition a to describe how the goods are being sold.
Why is comprate in the indicative mood instead of the subjunctive after se?
The conjunction se (if) only triggers the subjunctive when describing hypothetical or unlikely situations. Here, it introduces a factual requirement for the discount, which is a real condition (often called the first conditional). Therefore, it takes the standard present indicative.