[The Meaning of: “Whoever Sells and Buys … Has Sunk Into Usury”]

Answer—and Allah grants success: What appears to me is that what is intended by the hadith is the one who engages in trade; for it is of him, customarily, that such a phrase is said—“he sells and buys” or “he is selling and buying.” Accordingly, it does not include one who sells or buys not by way of trade, but to meet his personal need or his household’s, and the like.
What supports the soundness of what we have mentioned is his words at the end of the hadith: “has sunk into usury, then sunk into it,” for that befits those just mentioned, due to their frequent occupation with trade.
Moreover, traders are those who seek gains, profits, and the increase of wealth through buying and selling, so they are often exposed to falling into usury—unlike one who buys some need for his household, for he does not seek growth or profit; likewise one who seldom sells some need—such people rarely fall into usury.
Thus, it seems to me—and Allah knows best—that the phrase “he sells and buys” or “he sold and bought” is a general customary expression used to mean the one occupied with commerce. On that basis, customary usage takes precedence over purely linguistic usage.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2