The shopkeeper on Castle Street

The shopkeeper stands behind his counter on Castle Street's west stretch. He has something for sale.
Nudge 1Where to look
You need something to pay with: money, or something to sell at market.
Nudge 2A stronger push
Both are found in the game: one under the sea, one from a friend in the village.
Show the solutionThe whole answer, with a video
Drop the large gold coin (from the deep cave under the bay, In and out of the cave under the seabed) or the small pigmy cow (from Dylan, Dylan wants help) at the counter. The shopkeeper takes it and throws back a magic green bean: see A patch of earth that wants something planted.