Speaking as a buyer, when I need that one HQ item to advance, say, a Crafting Class, I don't have a need to buy it in bulk. If I see the -1- quantity item, and the end payment is less than buying any number greater than 1, then I will always go with that. Example.

1 (HQ) Blood Currant Tart - 1,000 = 1,000 gil
10 (HQ) Blood Currant Tart - 500 = 5,000 gil

If the end price is paying 1,000 gil for what I exactly need, or 5,000 gil with 9 items I don't need, I will go with the cheaper alternative.