Merchantable is a trade and law word. Goods are merchantable when they are in a fit state to be sold — not broken, not rotten, of the quality a buyer can reasonably expect. Older British law talked about ‘merchantable quality.’ Though actually, almost nobody says this in daily life. People say fit to sell or in good condition; modern consumer law often says satisfactory quality instead. You will meet merchantable in contracts, insurance, and commercial textbooks, not in a café. It describes goods, never people.